Download Physics 12 – Unit Exam 1

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Physics 12 – Unit Exam 1
Chapters 1 through 8
For the questions that require calculations, use the space provided for the question to show how you arrived
at your answer. You must show your work in order to receive credit for your answer. Use 10 m/s 2 as the
acceleration due to gravity at the surface of the earth.
1.
A car travels east away from the ocean on Pico Boulevard at a constant velocity of 15 m/s (~30 mi/hr).
How far will the car travel in 1 minute? (2)
DISTANCE = CONSTANT VELOCITY X TIME = 15 M/S X 60 S = 900 M
2.
A second car is stopped at the corner of 30th and Pico. The car accelerates away from the corner at 3
m/s2.
a.
After 6 seconds, how fast is the car traveling? (2)
SPEED INCREASES BY 3 M/S EVERY SEC – IN 6 SEC SPEED WILL BE 6 X 3 = 18 M/S
b.
How far did the car travel in the 6 seconds? (2)
AVG VELOCITY = (0 + 18)/2 = 9 M/S.
DISTANCE = AVG VELOCITY X TIME = 9 M/S X 6 SEC = 54 M
3.
The three balls shown are thrown straight upward with
different initial velocities.
a.
10 m/s
From slowest to fastest, rank the speeds of the balls 1
second after being thrown. (2)
B ( 0 M/S), C (5 M/S), A (10 M/S)
b.
20 m/s
From slowest to fastest, rank the accelerations of the
balls 1 second after being thrown. (2)
5 m/s
A
B
C
1 kg
2 kg
1.5 kg
ALL ACCELERATIONS ARE THE SAME – THE ACCELERATION DUE TO GRAVITY
4.
Car A accelerates from 40 to 50 mi/hr in 5 seconds. Car B accelerates from 0 to 50 mi/hr in 25 seconds.
Which car has a greater acceleration? (2)
BOTH HAVE THE SAME ACCELERATION -- A (10/5 = 2), B (50/25 = 2)
5.
A ball is thrown straight upward with a velocity of 20 m/s. Where is the ball located 3 seconds after
being thrown? (3)
AT 3 SECONDS THE VELOCITY IS (20 – 30) = -10 M/S DOWNWARD.
AVG VELOCITY = (20 + (-10))/2 = 5 M/S.
DISTANCE = AVG VELOCITY X TIME = 5 M/S X 3 SEC = 15 M ABOVE WHERE IT WAS THROWN.
6. Three blocks are shown with
horizontal forces acting on them.
a.
b.
10 N
A
2 kg
5N
5N
Rank them from the greatest net
force to the least net force. (2)
B (10 N), C (7 N), A (5 N)
5N
B
4 kg
10 N
5N
C
6 kg
Rank them from the greatest acceleration to the least acceleration. (2)
A and B (2.5 m/s2), C (1.2 m/s2)
c.
Rank them from the greatest inertia to the least inertia. (2)
C (6 kg), B (4 kg), A (2 kg)
7.
8.
A 20 kg box is being pulled to the right across the floor by a horizontal force of 400 N. Is the friction
force acting on the box greater than 400 N, equal to 400 N, or less than 400 N for the following
situations?
a.
The box is traveling at a constant speed. (2)
FRICTION = 400 N
b.
The box is traveling faster and faster. (2)
FRICTION LESS THAN 400 N
A 2 kg steel ball is stationary and suspended from the ceiling by a string.
a.
What does Newton’s First Law say about an object that is stationary? (2)
IF STATIONARY, THEN THE NET FORCE = 0
b.
Name the two forces acting on the ball and indicate the directions in which they point. (2)
FORCE THE STRING EXERTS ON THE BALL UPWARD
FORCE THE EARTH EXERTS ON THE BALL PULLING DOWNWARD (GRAVITY)
c.
Name the reaction forces to the forces in part b and indicate the directions in which they point. (2)
FORCE THE BALL EXERTS ON THE STRING PULLING DOWNWARD
FORCE THE BALL EXERTS ON THE EARTH PULLING UPWARD
9.
Suppose you are pushing a 100 kg box to the right across a smooth floor (no friction) with a horizontal
force of 200 N.
a.
How fast and in what direction is the box accelerating? (2)
ACCELERATION = FORCE/MASS = 200/100 = 2 M/S2, DIRECTION TO THE RIGHT
12 N
b.
When the box reaches a speed of 10 m/s, an additional second force of 200 N is applied to the block
but in the opposite direction to the first. Will the block speed up, remain traveling at the 10 m/s, or
slow down? Explain how you came to your conclusion. (3)
THE BOX WILL CONTINUE TO TRAVEL AT THE SAME SPEED OF 10 M/S. IN THIS CASE THE
NET FORCE IS ZERO, AND THEREFORE THE OBJECT WILL CONTINUE IN A STRAIGHT LINE
AT A CONSTANT SPEED ACCORDING TO NEWTON’S FIRST LAW.
10. Two identical sheets of paper are dropped – one that is wadded up and one that is not.
a.
Which one will have the greater force of air resistance acting on it? (2)
AIR RESISTANCE FORCE WILL BE THE SAME. WHEN TRAVELING DOWNWARD AT A
CONSTANT SPEED, THE NET FORCE MUST BE ZERO. WEIGHT = AIR RESISTANCE.
b.
Which one will have the greater terminal speed? (2)
THE WADDED PAPER – IT MUST TRAVEL FASTER TO HAVE THE SAME AIR RESISTANCE.
11. An airplane is flying due east at 200 km/hr. A strong
wind is blowing due south at 150 km/hr. In the box to
the right, draw vectors to represent the speed of the
airplane, the speed of the wind, and the resultant
direction of travel of the airplane. Estimate the ground
speed of the airplane. (3)
AIRPLANE
N
THE LENGTH OF THE ARROW
FOR THE NET EFFECT IS
APPROXIMATELY 250 KM/HR.
W
E
WIND
NET EFFECT
S
12. Three balls are shown to the right.
a.
A
5 kg
B
2 kg
C
8 m/s
Rank the balls from the greatest momentum to the least
momentum. (2)
C (9 KG M/S), A (8 KG M/S), B (7.5 KG M/S)
b.
1 kg
Rank the balls from the greatest impulse required to stop them to
the least impulse required to stop them. (2)
C, A, B IMPULSE = CHANGE IN MOMENTUM. THE GREATEST
CHANGE IN MOMENTUM IN THIS CASE IS THE GREATEST
MOMENTUM.
1.5 m/s
4.5 m/s
13. A ping pong ball and a bowling ball undergo a head-on collision. During the collision,
a.
which ball exerts a greater impulse on the other? (2)
IMPULSES WILL BE THE SAME
b.
which ball has the greater acceleration after the collision? Explain why. (3)
PING PONG BALL. BECAUSE THE IMPULSES ARE THE SAME AND THE TIME OF CONTACT
IS THE SAME, THE FORCES ARE THE SAME. WITH THE SAME FORCE, THE SMALLER
MASS WILL UNDERGO THE LARGER ACCELERATION.
14. Using the ideas of the impulse and momentum, explain why you move your hands backward when you
catch a raw egg tossed to you? (2)
WHEN CATCHING THE EGG YOU ARE CHANGING THE EGG’S MOMENTUM. THIS EQUALS THE
IMPULSE WHICH IS FORCE TIMES TIME. MOVING YOURS HANDS BACKWARD INCREASES THE
TIME REQUIRED TO STOP THE EGG AND THEREFORE DECREASES THE FORCE REQUIRED TO
STOP THE EGG. HOPEFULLY, THIS FORCE IS SMALL ENOUGH SO THAT IT DOESN’T BREAK
THE EGG.
15. A 120 kg football linebacker (football player) running to the right at 5 m/s tackles an 80 kg halfback
(another football player) who is running to the left toward the linebacker. The linebacker stops the
halfback “in his tracks.” (They stop, and the collision is totally inelastic.) At what speed was the
halfback running toward the linebacker? (2)
MOMENTUM IS CONSERVED. SO MOMENTUM BEFORE = (120 KG) x (5 M/S) + (80 KG) x
(UNKNOWN V) = MOMENTUM AFTER = ZERO BECAUSE THERE IS NO MOTION AFTER THE
COLLISION. MORE SIMPLY: (120) x (5) + (80) x V = 0. WHEN WE SOLVE FOR V, WE GET V = -7.5
M/S.
16. Two students, who both weigh 600 N, climb the stairs outside the physics lab. The first student climbs
the stairs in 5 seconds and the seconds climbs them in 8 seconds.
a.
Which student did more work? (2) WORK = FORCE x DISTANCE. BOTH EXERTED A FORCE
OF 600 N AND BOTH CLIMBED THE SAME VEFRTICAL DISTANCE, SO THE WORK DONE IS
THE SAME.
b.
Which student uses more power to do the work? (2) POWER = WORK/TIME. THE LESS TIME
THE MORE POWER WAS REQUIRED. SO, THE FIRST STUDENT USED MORE POWER.
17. Two balls have the same mass. The first ball is dropped and the second is thrown downward at 10 m/s.
When the balls are 2.5 m above the ground
a.
which ball has the greater kinetic energy? (2) THE THROWN BALL’S VELOCITY WILL ALWAYS
BE GREATER THAN THE DROPPED BALL’S VELOCITY. SO, THE THROWN BALL WILL HAVE
THE GREATER KINETIC ENERGY.
b.
which ball has the greater potential energy? (2) AT THE SAME HEIGHT (2.5 M) BOTH HAVE THE
SAME POTENTIAL ENERGY.
c.
which ball has the greater total energy? (2) BECAUSE THE KINETIC ENERGY OF THE THROWN
BALL IS GREATER THAN THE DROPPED BALL, AND BECAUSE THEIR POTENTIAL
ENERGIES ARE THE SAME, THE TOTAL ENERGY OF THE THROWN BALL WILL BE
GREATER.
18. The roller coaster ride starts from rest at point A.
Assume there is no friction or air resistance.
Rank the following from greatest to least:
a.
kinetic energy. (2) B, D, C, E, A
b.
potential energy. (2) A, E, C, D, B
A
E
C
c.
D
B
total energy. (2) SAME EVERYWHERE
19. Complete the table for a 2 kg ball thrown downwards with a speed of 10 m/s at time t = 0 sec. (4)
AT T = 0, KE = (1/2)x(2)x(10)2 = 100 J
AT T = 1, KE = (1/2)x(2)x(20)2 = 400 J
AT T = 2, KE = (1/2)x(2)x(30)2 = 900 J
Time
(seconds)
Kinetic Energy
(Joules)
Potential
Energy (Joules)
Total Energy
(Joules)
0
100
900-100 = 800
900
TOTAL ENERGY = KE + PE
1
400
900-400 = 500
900
2
900
0
900
AT T = 3, TE = 900 + 0 = 900 J.
ENERGY IS CONSERVED SO THAT
AT ALL TIMES TE = 900 J
PE THEN IS TE - KE
20. Suppose you are pulling on the rope with a force F and
lifting the 20 kg box vertically 0.5 m. (Ignore friction.)
F
a.
F
A, C, B (COUNT THE STRINGS SUPPORTIN THE
WEIGHT)
b.
F
Rank them from the greatest force you must exert to
the least force you must exert. (2)
Rank them from the greatest amount of work you
must do to the least amount of work you must do. (2)
A
B
WORK IS ALL THE SAME. YOU LIFTED THEM THE SAME DISTANCE
21
A hollow ring and a solid disk have the same radii and the same mass. They are released from rest at
the top of an inclined plane.
a.
Which one reaches the bottom first? (2) SOLID DISK – IT HAS A SMALL MOMENT OF INERTIA
b.
Suggest how the radius and the mass of the ring can be changed so that the result you obtained in
part a is reversed. (2)
YOU WANT TO REDUCE THE MOMENT OF INERTIA OF THE RING – MAKE THE RADIUS
SMALLER OR REDUCE THE MASS OF THE RING.
C
Rod A
22. Two rods appear to be identical, but their
center of masses are located in different
positions on the rod, as shown. What can
you tell me about the way the mass is
distributed in
a.
center of mass
Rod B
rod A? (2)
THE MASS IS EVENLY DISTRIBUTED OVER THE LENGTH OF THE ROD.
b.
rod B? (2)
HEAVY MATERIAL (LIKE STEEL) IS LOCATED THE LEFT OF THE C of M AND LIGHT
MATERIAL (LIKE WOOD) IS LOCATED TO THE RIGHT OF THE C of M.
25 N
23. A wrench is being used to loosen a nut from
the bolt. Rank the torques from greatest to
least.
A
25 N
B
10 N
C
A (25x10), C (10x20), B (25x7),
50 N
D (50x0)
7 cm
10 cm
10 cm
24. You are driving a car on a straight road at a constant
speed. You forgot that you put your physics book on
the roof your car, and you now make a turn to the
right.
D
E
C
a.
Indicate the path that your physics book takes
after it slides off the roof of your car. (2) D
b.
Name the centripetal force that is acting on the car.
(2)
B
A
FRICTION FORCE OF THE ROAD ON THE CAR.
c.
D
Name the corresponding centrifugal force. (2)
FRICTION FORCE OF THE CAR ON THE ROAD.
25. If a star that is spinning were to collapse and become a star with a smaller radius, what would happen
to the speed of rotation of the star? Explain why. (4)
THE SPEED OF ROTATION WILL INCREASE BECAUSE THE MOMENT OF INERTIA OF THE STAR
DECREASES. ACCORDING TO THE CONSERVATION OF ANGULAR MOMENTUM, THE SMALLER
THE MOMENT OF INERTIA OF A SPINNING BODY BECOMES, THE FASTER ITS ROTATIONAL
SPEED.