Download Physics 2010 Summer 2011 REVIEW FOR MIDTERM 2

Physics 2010
Summer 2011
REVIEW FOR MIDTERM 2
1.
A daredevil is going to jump over a canyon on his motorcycle. A river is 300.0 m below the cliff from
where he will start his jump. As he starts the jump, he leaves the launch ramp at 35° to the horizontal with
a velocity of Vo = 45.0 m/s The feat fails and he lands safely in the river. Neglect resistance.
A.
B.
What was his range?
What was his time of flight?
2.
A fire hose shoots water horizontally from the top of a building onto the wall of an adjacent building 31.0 m
away. The water leaves the nozzle of the hose at a speed of 6.40 m/s. How far below the level of the
nozzle does the water hit the wall?
3.
A.
A woman, of weight 45.0 kg, stands on a spring scale inside an elevator.
(1)
(2)
B.
4.
A 9.10 g bullet enter a 2.30 cm thick piece of plastic with a speed of 165 m/s. It passes through
the plastic and emerges with a speed of 92.0 m/s. How large is the average force exerted by the
bullet on the plastic?
Blocks 1 and 2 form a pulley system as shown. Block 1 (mass =
3.25 g) rests on the table and block 2 (mass = 1.90 g) is hanging
from the pulley. The table frictionless.
A.
B.
5.
What does the scale read when the elevator is accelerating upward at 3.65 m/s2?
What does the scale read when the elevator is accelerating downward at 2.70 m/s2?
Find the acceleration on the blocks.
What is the tension in the cord?
A 110 kg fullback runs at the line of scrimmage.
(a)
(b)
Find the constant force that must be exerted on him to bring him to rest in a distance of 1.0 m in a
time interval of 0.25 s.
How fast was he running initially?
6.
A small weight hangs from a string attached to the rearview mirror of a car. The car is accelerating at a rate
of 1.00 m/s2. At what angle does the string make with the vertical?
7.
Two blocks connected by a massless unstretched
string are on a horizontal surface and are connected to
a hanging weight by means of a string that passes
over a pulley. See figure.
(a)
(b)
Find the tension in string connected the two
blocks on the horizontal surface.
How much time is required for the hanging
weight to fall 10.0 cm if it starts from rest?
8.
A car rounds the top of a hill at a speed of 20.0 m/s. It briefly loses contact with the
pavement. This section of the road has an approximate circular shape (see
drawing). Find R.
9.
You are in Kenya standing on a cliff that is 9.0 m high. You are going to toss some food to a monkey
standing 3.5 m from the bottom of the cliff.
A.
B.
10.
If the food is thrown horizontally, what is the initial velocity needed to reach the monkey?
If you toss the food at an initial velocity of 3.3 m/s, what are the direction and magnitude of it
velocity 0.75 s later and just before it lands?
You are on the Kenai Peninsula in Alaska and you
want to cross the river to see an eagles nest. You cross
the river at an angle of 25.0° with a speed of 0.1 m/s.
The river is flowing 1.4 m/s. The width of the river is
10.0 m.
A.
B.
What is your velocity relative to the ground?
If you started directly across from the nest, how far will you have to walk to get to the nest after
exiting the river?
11.
You are riding a bike on the slick rock in Moab traveling fast at 16.1 m/s. You lock the wheels of your
mountain bike by applying the brakes. The coefficient of kinetic friction between the tires and the
sandstone is 0.720. How much time does it take to come to a halt?
12.
During a motocross accident a 16 year old male breaks his leg.
The leg is placed in a cast and traction device. Find the
magnitude of the force F exerted by the leg on the small
pulley. The mass is 2.5 kg.
13.
A University of Utah basketball player is running at 5.00 m/s directly toward the basket when he jumps into
the air to dunk the ball. He maintains his horizontal velocity.
(a)
(b)
What vertical velocity does he need to rise 0.750 meters above the floor?
How far from the basket (measured horizontally) must he start his jump to reach his maximum
height at the same time he reaches the basket?
14.
A.
Consider the 52.0 kg mountain climber in figure shown.
(a)
B.
Calculate the force that a mother must exert to hold her 12.0 kg child in an
elevator under the following conditions.
(a)
(b)
(c)
(d)
15.
(b)
(c)
Determine the coefficient of kinetic friction between m2 and the
incline.
Calculate the acceleration of each mass.
Find the tension in the string.
A car is traveling with a speed of 40.0 m/s up a hill
that has a slope of 10.0° above the horizontal. The
driver slams on his brakes to avoid going off a cliff
which is 65.0 m ahead. The brakes lock, and the car
slides up the hill and off the cliff. The coefficients of
static and kinetic friction between the tires and the
road are 0.8 and 0.6, respectively. The perfectly
vertical cliff is 32.0 m high, and has a large lake at
its base (shown in the figure). Do not worry--the
driver escapes the car unharmed.
(a)
(b)
(c)
(d)
17.
The elevator accelerates upward at 0.850 m/s2.
The elevator moves upward at a constant speed.
The upward bound elevator decelerates at 2.30 m/s2.
Calculate the ratio of the force to the weight of the child in each
case. Show the free body diagram used for this problem. (Note:
The diagram is the same for all parts.)
Masses m1 = 4.00 kg and m2 = 9.00 kg are connected by a light string that
passes over a frictionless pulley as shown in the figure. Mass m1 is held at
rest on the floor and mass m2 rests on a fixed incline of 2 = 40.0°. The
masses are released from rest, and m2 slides 1.00 m down the incline in 4.00
s.
(a)
16.
Find the tension in the rope and the force that the mountain climber
must exert with her legs on the vertical rock face to remain
stationary. Assume that the force is exerted parallel to her legs.
Also, assume negligible force exerted by her arms.
What is the speed of the car just as it is leaving the cliff?
What is the vertical component of the velocity of the car just before it hits the lake?
How far from the base of the cliff does the car hit the water?
What is the maximum height above the lake attained by the car?
A rescue plane wants to drop supplies to isolated hikers on a rocky
ledge in the Uinta Mountains east of Salt Lake City. The plane is
200 m above the climbers.
(a)
(b)
If the plane is traveling horizontally with a speed of 69 m/s
how far in advance (horizontal distance) must the goods be
dropped?
Now suppose the plane, traveling with the same velocity as
in part (a), releases the supplies a horizontal distance of 400
m in advance of the mountain climbers. At what vertical
velocity (up or down) should the supplies be released so
they arrive at the stranded climbers?
18.
A raft crossing the Colorado River can move in still water at a rate of
2.20 m/s. The raft must cross a 260 m section of the river and arrive at
a point up stream from where it starts. To do so, the pilot must head
the raft at an angle of 45° upstream. What is the speed of the current
of the river?
19.
Two buckets of sand hang from opposite ends of a rope that passes over a
pulley. One bucket is full and weighs 110 N, the other is only slight filled
and weighs 63 N.
(a)
(b)
20.
A person jumps from the roof of a house 4.0 m high. When she strikes the ground below, she bends her
knees so that her torso decelerates to a stop over an approximate distance of 0.70 m. If the mass of her
torso (excluding legs) is 50 kg, find
(a)
(b)
21.
her velocity just before her feet strike the ground;
the average force exerted on her torso by her legs during deceleration.
A daredevil is going to jump over a
river on his motorcycle. A ramp,
which is 2 m high at the take-off
point, is constructed on the left bank
of a 10 m wide river.
(a)
(b)
22.
Initially you hold on to the lighter bucket to keep it from moving.
What is the tension in the rope?
You release the bucket and the heavier bucket descends. What is
the tension in the rope now?
If the ramp has an angle of 2
= 20 ° and the daredevil’s
initial velocity is 20 m/s,
what is the highest the right bank can be for the stunt to still work?
Now the ramp has an angle of 45°. What initial velocity would the daredevil need to successfully
land on the right bank of the river [use the height found in part (a)].
In the drawing Robin Hood (mass = 75.0 kg) is about to escape from a
dangerous situation. With one hand, he is gripping the rope that holds
up a chandelier of mass 200 kg. When he cuts the rope where it is tied
to the floor, the chandelier will fall and he will be pulled up toward a
balcony 5 m above. Ignore friction between the rope and the beams
over which it slides and assume the rope is massless.
(a)
(b)
(c)
(d)
After Robin cuts the rope, what is his acceleration?
(Remember, acceleration is a vector.)
Find the tension in the rope while he escapes.
What is his velocity when he reaches the 5 m high balcony?
How long does it take Robin Hood to get from the ground to
the balcony after cutting the rope?
23.
A woman with a mass of 50 kg is standing on a metric scale of mass 3 kg in an elevator which
has a mass of 1000 kg on Earth.
(a)
(b)
(c)
(d)
24.
What does the scale read in Newtons when the elevator accelerates upward at 2.0 m/s2?
What does the scale read in Newtons when the elevator accelerates downward at 2.0
m/s2?
Find the tension in the cable while the elevator is accelerating upward.
If this elevator were on Mars (mass = 6.46 × 1023 kg, radius = 3.39 × 106 m), what
would the scale read when accelerating upward at 2.0 m/s2?
Nils is taking Lars on a sled ride. The coefficients of static and kinetic friction are :s = 0.40 and
:k = 0.20, respectively.
(a)
(b)
(c)
If initially at rest, what force must Nils use
to push Lars with an initial acceleration of
2.0 m/s2?
Once moving, what force must Nils pull
with to keep Lars moving at a constant
velocity?
After pulling Lars for while, Nils becomes tired so he lets go of the rope and jumps onto the sled.
Assuming they have a velocity of 2.0 m/s immediately after Nils jumps on, how far do the boys
slide before coming to rest?
mass of Nils = 40 kg; mass of Lars = 30 kg; mass of sled = 5 kg; 2 = 30°
25.
The lob in tennis is an effective tactic when your opponent
is near the net. It consists of lofting the ball over her head,
forcing her to move quickly away from the net (see the
drawing). Suppose that you loft the ball with an initial
speed of 15.0 m/s, at an angle of 50.0° above the horizontal.
At this instant your opponent is 10.0 m away from the ball.
She begins moving away from you 0.30 s later, hoping to
reach the ball and hit it back at the moment that it is 2.10 m
above its launch point.
(a)
(b)
(c)
(d)
26.
What maximum height above its launch point does
the ball reach?
What is the ball’s velocity at its maximum height?
What is the ball’s acceleration when it is 5m above its launch point?
With what minimum average speed must she move? (Ignore the fact that she can stretch, so that
her racket can reach the ball before she does.)
A skier is pulled up a slope by a tow bar at a constant acceleration of 0.500 m/s2. The slope is inclined at
25.0° with respect to the horizontal. The force applied to the skier by the tow bar is parallel to the slope.
The skier's mass is 50.0 kg, and the coefficients of static and kinetic friction between the skis and the snow
are 0.150 and 0.120 respectively.
(a)
(b)
(c)
What is the magnitude of the normal force that the skier experiences?
What is the magnitude of the force due to friction the skier feels?
Find the magnitude of the force that the tow bar exerts on the skier.
27.
Dawn stands on a scale in a glass elevator on Earth. Her mass is 50.0 kg, and the
combined mass of the elevator and scale is an additional 820 kg. Starting from rest, the
elevator is accelerated upward by a hoisting cable.
(a)
(b)
(c)
(d)
(e)
28.
In the drawing, the weight of block A is 425 N and the weight of block B is
215 N. Assume the pulley and cord are massless.
(a)
(b)
(c)
(d)
29.
After 3 seconds the elevator is moving upward at a speed of 9 m/s. As seen by
someone in an adjacent glass elevator moving downward at 5 m/s, what is
Dawn’s relative velocity?
What is Dawn’s acceleration?
What is the tension in the hoisting cable of the elevator while accelerating
upward?
What is Dawn’’s apparent weight while accelerating upward?
If this elevator were on Mars (mass = 6.26 × 1023 kg, radius = 3.39 × 106 m,
G = 6.673 × 10-11 N@m2/kg2), what would be Dawn’s apparent weight while
accelerating downward at 1.5 m/s2?
A.
Ignoring all frictional effects, what is the acceleration of the two
blocks?
Ignoring all frictional effects, what is the tension in the cord?
Assume there is friction between block A and the table. If the
blocks move at constant speed, what is the coefficient of kinetic
friction?
Assume there is friction between block A and the table. If the blocks move at constant speed,
what is the tension in the cord?
Using the information in the table below, approximately how much would a 100 kg man weigh on
the moon? [G = 6.67 × 10-11 Nm2/kg2]
Mass (kg)
Radius (km)
Sun
1.9 × 1030
696,000
Earth
5.97 × 1024
6,378
149,600,000
Moon
7.5 × 1022
1,738
384,400
(a) 17 N
B.
(b) 100 N
Orbital Radius (km)
(c) 170 N
(d) 1000 N(e) 1700 N
If the radius of the orbit of a satellite orbiting the earth is reduced by a factor of 2, the gravitational
force on the satellite will:
(a) decrease by a factor of 4
(d) increase by a factor of 2
(b) decrease by a factor of 2
(e) increase by a factor of 4
(c) remain the same
C.
An object of mass m resting on the surface of the earth experiences a force equal to its weight mg,
where g is the acceleration due to gravity. If M is the mass of the earth, G is the universal
gravitation constant, and R is the radius of the earth, which of the following expressions is equal to
g?
(a) GMm/R2
(b) GM/R2
(c) GMm/R
(d) GM/R(e) Gm/R2
D.
In a very tall building, an elevator with weight We moves quickly upward at a constant
acceleration a. Inside the elevator a woman with weight Ww is standing on a scale of weight Ws.
The entire weight of the elevator, woman and scale is supported by a single cable of tension T.
Which of the expressions below represents the apparent weight of the woman on the scale?
(a) T × (1 + a/g)
(b) (T × Ww)/(Ww + Ws + We)
(c) Ww (1 - a/g)
E.
(d) (Ww + We + Ws) × (1 + a/g)
(e) Ww × (g + a)
The diagram below shows two different masses hung from identical
Hooke’s law springs. The Hooke’s law constant k for the springs is
equal to:
(a) 2 N/cm
(b) 4 N/cm
(c) 5 N/cm
30.
(d) 10 N/cm
(e) 20 N/cm
The drawing shows a large cube (mass = 42 kg) being accelerated across a

horizontal table by a horizontal force P . The coefficient of kinetic friction
between the table and large cube is 0.24. A small cube (mass = 5.0 kg) is in
contact with the front surface of the large cube and will slide downward
unless

P is sufficiently large.
The coefficient of static friction between the
cubes is 0.71. What is the smallest magnitude that
keep the small cube from sliding downward?
31.

P
can have in order to
A skier goes down a hill that rises 30° above the horizontal. He jumps
off a ramp that has an angle of 60° above the horizontal with an initial
velocity of 15 m/s. The tip of the ramp is 4 m above the slope. (Note:
This is NOT the location where the skier lands.)
(a)
(b)
(c)
(d)
(e)
What is the maximum height above the ramp that he achieves?
What is his speed at the maximum height?
How long is the skier in the air?
What is the magnitude of his displacement as measured from
the end of the ramp to the spot he lands?
What is the final speed of the skier when he lands?

32.

P
An automobile engine has a weight W , whose magnitude is W = 3150 N. This engine is being positioned
above an engine compartment, as shown. To position the engine, a worker uses a rope to lower the engine
straight down.
(a)
The worker lowers the engine at a constant acceleration
of 0.25 m/s2 downward. Find the tension in the
supporting cable (T1) and the tension in the
positioning rope (T2).
(b)
(c)
As the worker has been lowering the engine, as
described in (a), it has been gaining speed. To slow the
engine down, he adjusts the force he applies such that
the engine has an acceleration with a magnitude of 0.5
m/s2. Find the new tension in the supporting cable (T1)
and the tension in the positioning rope (T2).
This skilled worker times the two-step lowering
procedure (as described above) perfectly so that as soon
as the engines speed is zero, it is in its final resting
place. The engine started from rest and the worker
spent 1.5 s in part (a) of the procedure. Initially how far
above the car was the engine?
33.
34.
A
The space rover Sojourner landed on Mars on July 4, 1997. The rover weighs 104 N on Earth.
What is the weight of Sojourner on Mars? [mass of Mars = 6.42 × 1023 kg; radius of Mars = 3400
km; G = 6.67 × 10-11 N@m2/kg2]
B.
The block (m = 5 kg) in the figure is pushed so that the
spring is compressed from equilibrium by 10 cm. The
spring constant is 100 N/m. What must be the minimum
coefficient of friction so that the block does not move
when it is let go? What type of friction is this?
C.
For each situation depicted, construct a free-body diagram for each object. Include labels and
arrows.
Two blocks are pulled across a frictionless horizontal surface (see drawing). Block B
does not slip
2.
Block is moving down an inclined plane at constant velocity.
A block is being pushed against a wall. The weight of the block in the drawing
is 64.4 N. The coefficient of static friction between the block and the vertical
wall is 0.500.
(a)
(b)
35.
1.
Calculate the minimum force F required to prevent the block from
sliding down the wall? [Hint: The static frictional force exerted on the
block is directed upward, parallel to the wall.]
Find the minimum force F required to start the block moving up the
wall. [Hint: The static frictional force is now directed down the wall.]
A golfer tees off and the ball is launched at a
speed of 40.0 m/s at an angle of 30° above the
horizontal. The ball lands on the green which is 5
meters above the tee.
(a)
(b)
(c)
(d)
(e)
How far from the tee did the ball hit the
ground?
What is the speed of the ball at its
highest point?
Find the maximum height of the ball.
Calculate the speed of the ball when it hit the green?
Find the angle the ball make when it hits the green with respect to the horizontal?
36.
In the drawing, the mass of block A is 43 kg and the weight of block B is 215 N. Assume the pulley and
cord are massless.
(a)
(b)
(c)
(d)
37.
38.
Ignoring all frictional effects, what is the acceleration of the two blocks?
Ignoring all frictional effects, what is the tension in the cord?
Assuming there is friction between block A and the table, if the
blocks move at constant speed, what is the coefficient of kinetic
friction?
Assuming there is friction between block A and the table, if the
blocks move at constant speed, find the tension in the cord.
A.
A hot air balloon is rising straight upward with a speed of 5.4 m/s. A ballast bag is released from
rest relative to the balloon when it is 11.6 m above the ground. How much time elapses before the
ballast bag hits the ground?
B.
The punter on a football team attempts to kick a football so that it stays in the air for a long “hang
time.” If the ball is kicked with an initial velocity of 25.6 m/s at an angle of 61.0° above the
ground, what is the hang time?
C.
A 18 g bullet is fired from a rifle. It takes 3.45 × 10-3 s for the bullet to travel the length of the
barrel and exits the barrel with a speed of 730 m/s. Assuming that the acceleration of the bullet is
constant, find the average net force exerted on the bullet.
D.
A rock of mass 44 kg accidentally breaks loose from the edge of a cliff and falls straight down.
The magnitude of the air resistance that opposes the downward motion of the rock is 272 N. Find
the magnitude of the acceleration of the rock.
A.
A golfer hits the ball with speed of 33.9 m/s. The ball travels the maximum possible distance
before landing on the green. The tee and the green are at the same elevation. Ignore air resistance.
(1)
(2)
(3)
B.
A rock climber throws a small first aid kit to another climber who is higher up the mountain. The
initial velocity of the kit is 14 m/s at an angle of 74° above the horizontal. At the instant the kit is
caught, it is traveling horizontally and has a vertical speed of zero. Ignore air resistance.
(1)
(2)
39.
A.
What is the longest “hole-in-one” that the golfer can make if the ball does not roll when
its hits the green?
What is the maximum height of the ball?
What is the velocity of the ball when it hits the ground? (Velocity is a vector.)
What is the vertical distance between the two climbers?
What is the horizontal distance between the two climbers?
Two large crates (m1 = 120 kg, m2 = 180 kg) are hung by strong massless cables as shown in
the drawing. A tension (T = 3.60 × 103 N) is applied to the upper cable which accelerates the
load upward.
(1)
(2)
Find the upward acceleration of the two-crate load.
What is the tension in the cable between the upper and lower crates?
B.
A student presses a book between his hands as shown in the drawing. The
forces that he exerts on the front and back covers of the books are perpendicular
to the book and are horizontal. The book weighs 36 N. The coefficient of static
friction between his hands and book is 0.45. To keep the book from falling,
what is the magnitude of the minimum pressing force that each hand must
exert?
C.
A car is traveling at a speed of 15.6 m/s. The driver suddenly slams on his brakes and locks the
wheels. The coefficient of kinetic friction between the tires and the road is 0.630. What is the
speed of the automobile after 2.00 s have elapsed. Ignore the effect of air resistance.
40.
A.
A block with a spring attached is being pushed by the end of the spring
perpendicularly to a vertical wall as shown in the drawing. The spring is pushed until the
block does not slip downward on the wall and the spring is compressed
by 0.079 m. If the same block-spring combination is held vertically, the
spring stretches by 3.34 cm. What is the coefficient of static friction
between the block and the wall?
B.
A crate is sliding down an inclined plane at an angle of 27.6° above the horizontal. The coefficient
of kinetic friction between the crate and the surface of the ramp is 0.463.
(1)
(2)
(3)
Find the acceleration of the crate.
If the crate makes it to the horizontal floor, what is its acceleration?
Is it possible that the block will not make it to the floor because it stops?
41.
A.
B.
C.
D.
42.
43.
44.
A.
A bowling ball (mass = 7.2 kg, radius = 0.14 m) and a ball (mass = 3.1 kg,
radius = 0.028 m) may each be treated as uniform spheres. What is the magnitude of the
maximum gravitational force that each can exert on the other?
When a projectile is launched at an angle of 10.5° above the horizontal the highest barrier
that the projectile can clear is 11.0 m. What is the projectile's launch speed?
An arrow, starting from rest, leaves the bow with a speed of 12.0 m/s. If the average force
exerted on the arrow by the bow were doubled, all else remaining the same, with what
speed would the arrow leave the bow?
A rock of mass 47 kg accidentally breaks loose from the edge of a cliff and falls straight
down. The magnitude of the air resistance that opposes its motion is 226 N. What is the
magnitude of the acceleration of the rock?
Two forces, F1 and F2, act on the 5.00 kg block shown in the
drawing. The magnitudes of the forces are F1 = 59.0 N and
F2 = 70.5 N. The coefficient of kinetic friction between the floor
and the block is 0.20 and the coefficient of static friction
between the block and the floor is 0.30. What is the horizontal
acceleration (magnitude and direction) of the block?
F1
65E
B.
A 3.60 kg box is sliding across the horizontal floor of an elevator. The coefficient of
kinetic friction between the box and the floor is 0.370. Determine the kinetic frictional
force that acts on the box when the elevator is accelerating downward with an
acceleration whose magnitude is 1.70 m/s2.
A.
The drawing shows a circus clown who weighs 920 N. The coefficient of
static friction between the clown's feet and the ground is 0.41 and the
coefficient of kinetic friction between the clown’s feet and the ground is
0.30. He pulls vertically downward on a rope that passes around three
pulleys and is tied around his feet. What is the minimum pulling force that
the clown must exert to yank his feet out from under himself?
B.
A neutron star has a mass of 2.0 1030 kg (about the mass of our sun) and a radius of
4.6 103 m (about the height of a good-sized mountain). Suppose a block falls from rest
near the surface of such a star. How fast would it be moving after it has fallen a distance
of 0.012 m? (Assume that the gravitational force is constant over the distance of the fall,
and that the star is not rotating.)
A car is traveling with a speed of 40.0 m/s up a hill that has a slope of 20.0° above the horizontal
when he realizes that he is near the edge of the cliff. For some reason, his car will not get out of
cruise control so he reaches the edge of the cliff with the same speed. The perfectly vertical cliff
is 32.0 m high, and has a large lake at its base (shown in the figure). Do not worry--the driver
escapes the car unharmed. Neglect air resistance.
A.
B.
C.
D.
E.
What is the speed of the car when it reaches the greatest height above the lake?
What is the maximum height of the car above the water?
What is the speed of the car just before it hits the lake?
What is the angle that the car’s velocity makes with the water just before it hits the water?
How far from the base of the cliff does the car hit the water?
F2
45.
A.
Two large crates (m1 = 120 kg, m2 = 180 kg) are hung by strong massless
cables as shown in the drawing. A tension (T = 3.60 × 103 N) is applied to the
upper cable which accelerates the load upward.
1.
2.
46.
47.
Find the upward acceleration of the two-crate load.
What is the tension in the cable between the upper and lower crates?
B.
A student presses a book between his hands as shown in the drawing. The forces
that he exerts on the front and back covers of the books are perpendicular to the
book and are horizontal. The book weighs 36 N. The coefficient of static friction
between his hands and book is 0.45. To keep the book from falling, what is the
magnitude of the minimum pressing force that each hand must exert?
C.
A car is traveling at a speed of 15.6 m/s. The driver suddenly slams on his brakes and
locks the wheels. The coefficient of kinetic friction between the tires and the road is
0.630. What is the speed of the automobile after 2.00 s have elapsed. Ignore the effect of
air resistance.
A.
The block in the drawing is initially at rest. Two forces, F1
and F2, then act on the 5.00 kg block shown in the drawing.
The magnitudes of the forces are F1 = 59.0 N and F2 = 70.5
N. The coefficient of kinetic friction between the floor and
the block is 0.20 and the coefficient of static friction
between the block and the floor is 0.30. What is the
horizontal acceleration (magnitude and direction) of the
block 1 second after the forces were initially applied.
B.
A 3.60 kg box is sliding across the horizontal floor of an elevator. The coefficient of
kinetic friction between the box and the floor is 0.370. Determine the kinetic frictional
force that acts on the box when the elevator is accelerating downward with an
acceleration whose magnitude is 1.70 m/s2.
A.
A box of mass 2.55 kg is suspended by a spring from the ceiling.
The spring is stretched 1.50 m from its relaxed length. The box is
also tied to the ground below by a massless string that has a tension
of 12.5 N.
1.
2.
B.
What is the spring constant of the spring?
If the string were cut, what would be the initial acceleration
of the box?
Starting from rest, a penguin weighing 50.0 N slides down a steep hill at an angle of
53.1° below horizontal. The ice has a coefficient of kinetic friction
of 0.80.
1.
2.
What is the magnitude of the normal force exerted by the
hill on the penguin?
How far down the hill will the penguin travel in
2.00 seconds?
48.
In a circus trick a clown is fired from a cannon at an angle of 36.9° from the horizontal with an
initial velocity of 15.0 m/s. At the same time 12.0 m away a hoop is thrown vertically into the air
from the same initial height as the cannon. Ignoring the size of the clown and the hoop answer
the following:
A.
B.
C.
D.
49.
50.
What is the maximum height above the cannon that the clown reaches?
What must the initial velocity of the hoop be so that the clown passes through the hoop
(you can ignore the sizes of the clown and the hoop)?
How long after the clown is fired will he pass through the middle of the hoop?
How high above the initial height will the clown be when he passes through the hoop?
A.
In the amusement park ride known as Magic Mountain Superman, powerful magnets
accelerate a car and its riders from rest to 45 m/s (about 100 mi/h) in a time of 4.1 s. The
mass of the car and riders is 5.5 × 103 kg. Find the average net force exerted on the car
and riders by the magnets
B.
The block (m = 5 kg) in the figure is pushed so that the spring
is compressed from equilibrium by 10 cm. The spring
constant is 100 N/m. What must be the minimum coefficient
of friction so that the block does not move when it is let go?
C.
An 81 kg baseball player slides into second base. The coefficient of kinetic friction
between the player and the ground is 0.47. If the player comes to rest after 1.6 s, what
was his initial velocity?
D.
A rock climber throws a small first aid kit to another climber who is higher up the
mountain. The initial velocity of the kit is 14 m/s at an angle of 74° above the horizontal.
At the instant the kit is caught, it is traveling horizontally and has a vertical speed of zero.
Ignore air resistance. What is the horizontal distance between the two climbers?
A.
Two forces, F1 and F2, act on the 5.00 kg block shown in the
figure and the block slides. The magnitudes of the forces are
F1 = 59.0 N and F2 = 70.5 N. The coefficient of kinetic
friction between the floor and the block is 0.20. What is the
horizontal acceleration (magnitude and direction) of the
block?
B.
A 65.0 kg crate rests on a level floor at a shipping dock. The coefficients of static and
kinetic friction are 0.790 and 0.450, respectively.
1.
2.
What horizontal pushing force is required to just start the crate moving?
Assume the force you found in part 1 is applied for 10 seconds (use 400 N if you
did not find an answer to 1). How far has the crate moved in 10 seconds?
51.
A.
Two large crates (m1 = 120 kg, m2 = 180 kg) are hung by strong massless
cables as shown in the drawing. A tension (T = 2.40 × 103 N) is applied to
the upper cable.
1.
2.
Find the acceleration of the two-crate load.
What is the tension in the cable between the upper and
lower crates?
52.
B.
A 73 kg person is standing on a scale in an elevator with an acceleration of 1.4 m/s2. The
person is moving upwards and coming to a stop. What does the scale read during this
acceleration?
C.
In the drawing, the weight of the block A on the table is
446 N and that of the hanging block B is 185 N. Ignore all
frictional affects, and assume the pulley is massless. Find
the tension in the cord.
A.
Superman drives a car off the edge of a cliff that is 48 m high at an angle 10 degrees
above the horizontal. The car is traveling 42.8 m/s when it leaves the cliff.
1.
2.
3.
53.
How fast is the car traveling when it reaches the highest point of its travel?
How far from the base of the cliff does the car land?
How fast is the car traveling when it lands?
B.
You have discovered a new planet, Kzyz, which has a mass 9 times the mass of Earth
and 6 times the radius of Earth. What is the acceleration due to gravity on the surface of
this new planet?
A.
A 15 g bullet is fired from a rifle. It takes 2.10 × 10 -3 s for the bullet to travel the length
of the barrel, and it exits the barrel with a speed of 701 m/s. Assuming that the
acceleration of the bullet is constant, find the average net force exerted on the bullet.
B.
The helicopter in the drawing is moving horizontally to the right at a constant
velocity. The weight of the helicopter is W = 58200 N. The lift force L
generated by the rotating blade makes an angle of θ = 21.0° with respect to the
vertical. Determine the magnitude of the air resistance R that opposes the
motion.
C.
An 81 kg baseball player slides into second base. The coefficient of kinetic friction
between the player and the ground is 0.47. If the player comes to rest after 1.6 s, what
was his initial velocity?
D.
In a mall, a shopper rides up an escalator between floors. At the top of the escalator, the
shopper turns 90° to the right and walks 13.29 m to a store. The magnitude of the
shopper's displacement from the bottom of the escalator to the store is 16.0 m. The
vertical distance between the floors is 6.14 m. At what angle is the escalator inclined
above the horizontal?
54.
55.
56.
A.
Forces, F1 and F2, act on the 5.00 kg block shown in the drawing, and the block slides.
The magnitudes of the forces are F1 = 59.0 N and F2 = 70.5 N. The coefficient of kinetic
friction between the floor and the block is 0.20. What is the horizontal acceleration
(magnitude and direction) of the block?
B.
A helicopter flies over the arctic ice pack at a constant
altitude, towing an airborne 116-kg laser sensor that
measures the thickness of the ice (see the drawing). The
helicopter and the sensor both move only in the horizontal
direction and have a horizontal acceleration of magnitude
2.98 m/s2. Ignoring air resistance, find the tension in the
cable towing the sensor.
C.
You are traveling in a convertible with the top down. The car is moving at a constant
velocity 26.4 m/s, due east along flat ground. You throw a tomato straight upward at a
speed of 10.8 m/s. How far has the car moved when you get a chance to catch the
tomato?
A.
The drawing shows box 1 resting on a table, with box 2 resting on top of
box 1. A massless rope passes over a massless, frictionless pulley. One
end of the rope is connected to box 2, and the other end is connected to
box 3. The weights of the three boxes are W1 = 53.5 N, W2 = 36.6 N, and
W3 = 25.2 N. Determine the magnitude of the normal force that the table
exerts on box 1.
B.
A rocket blasts off from rest and attains a speed of 46 m/s in 13 s. An astronaut has a
mass of 53.3 kg. What is the astronaut's apparent weight during take-off?
C.
A block with a spring attached is being pushed by the end of the spring
perpendicularly to a vertical wall as shown in the drawing. The spring
is pushed until the block does not slip downward on the wall and the
spring is compressed by 0.079 m. If the same block-spring
combination is held vertically, the spring stretches by 3.34 cm. What is
the coefficient of static friction between the block and the wall?
A.
Superman drives a car off the edge of a cliff that is 50.0 m high at an angle 37.0 degrees
above the horizontal. The car was traveling 50.0 m/s when it left the cliff.
1.
2.
3.
B.
How fast was the car traveling when it reaches the highest point of its travel?
How far from the base of the cliff did the car land?
How fast was the car traveling when it landed?
You have discovered a new planet Styxx which is 20 times the mass of Earth and 5 times
the radius of Earth. What is the acceleration due to gravity on the surface of this new
planet?