Download 1) Whereas Aristotle relied on logic in explaining nature, Galileo

SCI 3101
Test I
MULTIPLE CHOICE. (3 points each)
1)
Whereas Aristotle relied on logic in explaining nature, Galileo relied on:
A) experiment.
B) patterns.
C) logic also.
D) mathematics.
2)
Your weight is
A) the gravitational attraction between you and the earth.
B) a property of mechanical equilibrium.
C) actually your mass.
D) all of these
E) none of these
3)
A 1-kg mass at the earth's surface weighs about
A) 9.8 N.
B) 14.7 N.
C) 1 N.
D) 4.9 N.
Which has zero acceleration? An object
A) moving at constant velocity.
C) in mechanical equilibrium.
E) none of these
4)
B) at rest.
D) all of these
5)
A car accelerates from rest at 2 m/s2. What is its speed 3 s after the car starts moving?
A) 3 m/s
B) 6 m/s
C) 2 m/s
D) 4 m/s
6)
It takes 6 s for a stone to fall to the bottom of a mine shaft. How deep is the shaft?
A) about 60 m
B) about 120 m
C) more than 200 m D) about 180 m
7)
A sheet of paper can be withdrawn from under a container of milk without toppling it if the
paper is jerked quickly. This best demonstrates that
A) the milk carton has no acceleration.
B) there is an action-reaction pair of forces.
C) the milk carton has inertia.
D) gravity tends to hold the milk carton secure.
8)
A hockey puck is set in motion across a frozen pond. If ice friction and air resistance are
neglected, the force required to keep the puck sliding at constant velocity is
A) 0 N.
B) the weight of the puck divided by the mass of the puck.
C) equal to the weight of the puck.
D) the mass of the puck multiplied by 10 m/s/s.
E) none of these
9)
A 10-N falling object encounters 4 N of air resistance. The magnitude of the net force on the
object is
A) 6 N.
B) 0 N.
C) 10 N.
D) 4 N.
10) A bag of groceries has a mass of 10 kg and a weight of about
A) 1000 N.
B) 980 N.
C) 9.8 N.
D) 98 N.
11) A heavy object and a light object are dropped at the same time from rest in a vacuum. The
heavier object reaches the ground
A) at the same time as the lighter object.
B) sooner than the lighter object.
C) later than the lighter object.
12) A 500-N parachutist opens his chute and experiences an air resistance force of 800 N. The net
force on the parachutist is
A) 800 N downward.
B) 300 N downward.
C) 500 N downward.
D) 300 N upward.
13) A freight train rolls along a track with considerable momentum. If it rolls at the same speed but
has twice as much mass, its momentum is
A) unchanged.
B) zero.
C) quadrupled.
D) doubled.
14) Compared with falling on a wooden floor, a wine glass may not break when it falls to a
carpeted floor because of the
A) longer time to stop.
B) lesser impulse in stopping.
C) both of these
D) neither of these
15) A ball is moving at 4 m/s and has a momentum of 48 kg(m)/s. What is the ball's mass?
A) 48 kg
B) 4 kg
C) 192 kg
D) 12 kg
16) A rifle of mass 2 kg is suspended by strings. The rifle fires a bullet of mass 1/100 kg at a
speed of 200 m/s. The recoil velocity of the rifle is about
A) 0.001 m/s.
B) 0.01 m/s.
C) 0.1 m/s.
D) 1 m/s.
17) An object is raised above the ground gaining a certain amount of potential energy. If the same
object is raised twice as high, it gains
A) four times as much potential energy.
B) twice as much potential energy.
C) neither of these
18) According to Newton, the greater the masses of interacting objects, the
A) greater the force between them by the square of the masses.
B) greater the gravitational force between them.
C) less the gravitational force between them.
19) A woman who normally weighs 400 N stands on top of a very tall ladder so she is one Earthradius above the earth's surface. How much would she weigh there?
A) 100 N
B) 200 N
C) 400 N
D) zero
20) Which is most responsible for the ocean tides?
A) the Sun
B) the Moon
C) both contribute equally
21) A rock is thrown upward at 50o with respect to the horizontal. As it rises, its horizontal
component of velocity
A) decreases.
B) increases.
C) remains unchanged.
22) A gun with a muzzle velocity of 100 m/s is fired horizontally from a tower. Neglecting air
resistance, where will the bullet be 1 s later?
A) 490 m downrange
B) 100 m downrange
C) 50 m downrange
D) 98 m downrange
23) An airplane flies at 40 m/s at an altitude of 50 m. The pilot drops a heavy package, which falls
and strikes the ground. Where, approximately (i.e. neglecting air resistance), does the package
land?
A) 500 m behind the plane
B) beneath the plane
C) 400 m behind the plane
D) more than 500 m behind the plane
24) Two projectiles are fired at equal speeds but different angles. One is fired at an angle of 30o
and the other at 60o. The projectile to hit the ground first will be the one fired at (neglect air
resistance)
A) 60o.
B) 30o.
C) Both hit at the same time.
25) A bullet fired horizontally hits the ground in 0.5 s. If it had been fired with twice the speed in
the same direction, it would have hit the ground in
A) 0.5 s.
B) less than 0.5 s.
C) more than 0.5 s.
Problems (SHOW ALL WORK ON THE ANSWER SHEET):
1. (5 points) A horizontal force of 100N is required to push a box across a floor at constant
velocity.
What is the net force acting on the box?
0N
How much is the friction force that acts on the box?
100 N
2. (5 points) A rocket of mass 100,000kg undergoes an acceleration of 2 m/s 2. Calculate the
force being developed by the rocket engines.
F = m (a )
= 100,000kg (2m / s 2 )
= 200,000 N
3. (5 points) This question is typical on some driver’s license exams: A car moving at 50 km/h
skids 15m with locked brakes. How far will the car skid with locked brakes at
150km/h?
To answer this problem you need to compare the kinetic
energy at each speed.
1
m( 3v )2
2
1
KE 50 = mv 2
2
mass is the same so it cancels
KE150 =
KE150 ( 3v )2
= 2
KE 50
v
=9
Since there is a 9 fold increase in kinetic energy by a 3x speed
increase, there is a 9 fold increase in stopping distance, so the
skid will be:
9 x 15m = 135m
4. (5 points) How much work is done in lifting a 100N block of ice a vertical distance of 2
meters?
W =F•D
= 100 N • 2 m
= 200 J
5. (5 points) What is the efficiency of a pulley system that will raise a 2000N load a vertical
distance of 1m when 3000J of effort is involved?
W 
eff =  out 
 Win 
but first need to calculate Wout
Wout = F • d
= 2000 N • 1m
= 2000 J
 2000 J 
eff = 

 3000 J 
= 0.67