First Exam for Physics 102, Section 1, Fall 2005
9/14/2005
Notes:
1) Always assume g=10 m/s2 for the gravitational acceleration on the Earth’s surface.
2) For a couple of the problems, you will need the formula for the distance that is traveled by something that
1
has a constant acceleration when it starts from zero velocity: d = at 2 .
2
1.
2.
3.
4.
Science is a body of knowledge that
A) describes order in nature
B) is an ongoing activity of humans
C) condenses knowledge into testable laws
D) all of the above choices are correct
E) none of the above choices are correct
The property that an object at rest tends to remain at
rest unless perturbed by a force was found by
Galileo, who named this property:
A) Violent Motion
B) Inertia
C) Quintessence
A truck is moving at constant velocity. Inside the
storage compartment, a rock is dropped from the
midpoint of the ceiling and strikes the floor below.
The rock hits the floor
A) exactly below the midpoint of the ceiling
B) ahead of the midpoint of the ceiling
C) behind the midpoint of the ceiling
D) more information is needed to solve this
problem
E) none of these
If you whirl a rock at the end of a string, it will
follow a circular path. If the string breaks the
tendency of the rock is to
A) continue to follow a circular path
B) follow a straight-line path
C) increase its speed
D) revolve in a smaller circle
5.
What is the Net Force on the block?
10 N
A) –10N
B) +10N
C) 30N
6.
20 N
“+” direction
We can use the Equilibrium rule to determine
unknown forces on objects which are not
accelerating. Use the Equilibrium Rule to calculate
the Friction Force if the block is sliding in a straight
line at constant velocity
pulling force
20N
friction force
A) zero
B) 20 N
C) cannot say
7.
Use the Equilibrium Rule to Determine the Unknown
Force on the Painter’s platform, which is at rest
11. A ball is thrown straight up in the air. Gravity makes
the ball fall back down again. What is the
acceleration of the ball at the top of its trajectory?
A) 10 m/s2 upward
B) zero
C) 10 m/s2 downward
D) can’t say
12. What is the average speed of a cheetah that sprints
100 m in 5 s?
A) 500 m/s
B) 20 m/s
C) 0.05 m/s
D) can’t say
A) 400 N
B) 450 N
C) 850 N
8.
9.
Consider a pair of forces, one having a magnitude of
30 N, and the other 23 N. What minimum net force is
possible for these two forces?
A) 53 N
B) 7 N
C) 23 N
D) 30 N
E) 0 N
The two measurements necessary for calculating
average speed are
A) acceleration and time
B) velocity and time
C) distance and time
D) distance and acceleration
E) velocity and distance
10. A ball is thrown upwards. Neglecting air resistance,
what initial upward speed does the ball need to
remain in the air for a total time of 10 seconds?
A) about 50 m/s
B) about 60 m/s
C) about 80 m/s
D) about 100 m/s
E) about 110 m/s
13. Car A moves East at 100 km/hr, Car B moves West
at 100 km/hr. The cars have
A) the same speed and the same velocity
B) the same speed but different velocities
C) different speeds and different velocities
D) none of the above
14. A rock falls off a cliff. What is its speed after 10 s?
(neglect air resistance)
A) 10 m/s
B) 50 m/s
C) 100 m/s
15. Acceleration is defined as Δv/Δt. What are the units
of acceleration?
A) Length
B) Length/Time
C) Length/(Time2)
D) Mass % (Length/Time)
16. A car goes from rest to 100 km/hr in 5 s. What is its
average acceleration for those 5 s?
A) 500 (km/hr)/s
B) 20 (km/hr)/s
C) 10 (km/hr)/s
17. A kilogram is a measure of an object’s
A) weight
B) force
C) mass
D) size
18. Strange as it may seem, it is just as hard to accelerate
a car on a level surface on the moon as it is here on
the Earth. This is because
A) the mass of the car is independent of gravity
B) the weight of the car is independent of
gravity
C) Nonsense! A car is much more easily
accelerated on the moon than on the Earth.
19. Gravity on the surface of the moon is only 1/6 as
strong as gravity on the Earth. What is the mass of a
60-kg object on the moon?
A) zero
B) 10 kg
C) 60 kg
D) can’t say, need more information
24. A 200 kg skydiver and a 100 kg skydiver, equipped
with the same size parachutes, both jump from the
same height. Which one experiences greater force
from air drag?
A) the lighter one
B) the heavier one
C) both the same
D) can’t say.
25. Joe pushes Bill, who is asleep. Bill
A) will inevitably push Joe when he wakes
B) pushes Joe immediately, but not as hard
C) does not push even after he wakes up
D) pushes Joe equally hard even without
waking up
20. You push on a crate that is sliding across the floor.
You push with a constant force, and there is no
friction acting on the crate. The crate accelerates at
1m/s2. If you push 4 times as hard, what will the
acceleration of the crate be?
A) 2 m/s2
B) 4 m/s2
C) can’t say
26. As a ball falls, the action force is the pull of the
Earth’s mass on the ball. The reaction force is the
A) air resistance acting against the ball
B) acceleration of the ball
C) pull of the ball’s mass on the Earth
D) none of these
21. A 747 cruises at constant velocity and the thrust force
of the engines is 105 pounds total. How much force
is air drag exerting on the plane? (magnitudes)
A) 105 pounds
B) zero pounds
C) can’t say
27. Your friend says that the heavyweight champion of
the world cannot exert a force of 50 N on a piece of
tissue paper with his best punch. The tissue paper is
held in midair—no wall, no tricks. You
A) agree that it can’t be done
B) have reservations about this assertion
C) disagree, for a good punch easily delivers
this much force
22. What is the acceleration of the plane in the previous
question?
A) zero
B) 105 pounds divided by the mass of the plane
C) can’t say
23. How does the gravitation force on a falling body
compare with the air drag force before the falling
body reaches terminal velocity?
A) gravitation force is less than air drag force
B) the two forces are equal
C) gravitation force is bigger than air drag force
D) can’t say, need more information
28. A ballplayer hits a ball with a bat. The action force is
the impact of the bat against the ball. The reaction to
this force is the
A) air resistance on the ball
B) weight of the ball
C) force that the ball exerts on the bat
D) grip of the player’s hand against the ball
E) weight of the bat
29. To produce a net force on a system, must there be an
externally applied force?
A) No
B) Yes
C) It depends
30. If the forces that act on a bullet and the recoiling gun
from which it is fired are equal in magnitude, why do
the bullet and the gun have very different
accelerations?
A) They experience different impulses
B) They have different masses
C) The momentum is concentrated in the bullet
31. Consider the two forces acting on the person who
stands still, namely, the downward pull of gravity on
the person and the upward support of the floor. Do
these two forces form an action-reaction pair?
A) Yes
B) No
32. If you stand next to a wall on a frictionless
skateboard and push the wall with a force of 30N,
how hard does the wall push on you?
A) 0 N
B) 30 N
C) 60 N
D) can’t say
33. You’re driving down the highway and a bug spatters
into your windshield. Which undergoes the greater
change in momentum during the time of contact?
A) the bug
B) your car
C) both the same
34. Which has more momentum, a 1-ton car moving at
100 km/h or a 2-ton truck moving at 75 km/h?
A) the car
B) the truck
C) can’t say
D) both the same
35. A baseball player loses his mitt running to the
outfield to catch a ball. To minimize the force of
impact, when he’s catching the ball he should
A) move his hand back from the ball,
maximizing impact duration
B) move his hand toward the ball, minimizing
impact duration
C) neither makes any difference
36. A baseball player loses his mitt running to the
outfield to catch a ball. To minimize the impulse of
impact, when he’s catching the ball he should
A) move his hand back from the ball,
maximizing impact duration
B) move his hand toward the ball, minimizing
impact duration
C) neither makes any difference
37. A rubber ball and a small bag of sand each have the
same weight. They are dropped from the same height
onto a hard floor. The rubber ball bounces and the
sand bag doesn’t. Which one receives the greater
impulse?
A) the small bag of sand
B) the ball
C) both are the same
D) can’t say, need more information
38. A man holding a basketball is standing on frictionless
ice. He throws the the ball to the side. Which one
gets the bigger change in momentum?
A) the ball
B) the man
C) both are the same
D) can’t say, need more information
39. A 15-ton railroad car is moving at 2 m/s when it
slams into and links with another 15-ton railroad car
that is stationary. How fast does the pair of linked
cars move after the collision, assuming we can
neglect all sources of drag?
A) 0.5 m/s
B) 1 m/s
C) 2 m/s
D) can’t say, need more information
40. A 5,000 kg freight car moving at 2 m/s runs into a
10,000 kg freight car at rest. They couple upon
collision and move away as one body at
A) 2 m/s
B) 1 m/s
C) 2/3 m/s
D) 1/3 m/s