Post on 20-May-2018
South Pasadena • AP Physics Name _______________________________
Period ___ Date ___/___/___
PRACTICE TEST for Midterm Exam
FORMULAS
d = vt d = vot + ½ at2 d =
vo + v
2 t v = vo + at v2 = vo
2 + 2ad
v = vx2 + vy
2 = tan–1
vy
vx vx = v cos vy = v sin
dx = vxt vy = voy + at dy = voyt + ½ at2 vy2 = voy
2 + 2ady
F = ma W = mg P = F
A F = mgsin g = −9.8 m/s2
freq = rev
t v = 2 π r (freq) aC =
v2
r FC =
mv2
r π = 3.14
FG = G mM
r2 FS ≤ μS N FK = μK FN G = 6.67 × 10–11
N·m2/kg2
p = mv I = ∆p = m(v – v0) = Ft pbefore = pafter
KE = ½ mv2 PE = mgh W = F·d = ∆KE P = W
t KE = ½ mv2
IMA = Fout
Fin =
din
dout AMA =
Fout-actual
Fin-actual Eff =
AMA
IMA × 100% PEbefore + KEbefore = PEafter + KEafter
Use these terms to identify each description given in terms 1-12 below:
Acceleration Centripetal Acceleration Centripetal Force
Coefficient of Friction Displacement Distance
Energy Force Force of Friction
Frequency Gravitational Force Gravitational Potential Energy
Impulse Kinetic Energy Mass
Momentum Normal Force Position
Power Pressure Speed
Tension Time Velocity
Weight Work
Description Quantity Vector/Scalar Units
1 A push or pull perpendicular to
an object’s motion. Centripetal force Vector N or
kg·m
s2
2 The attraction between two
objects due to their masses. Gravitational Force “Vector” N or
kg·m
s2
3 The change in an object’s
kinetic energy. Work Scalar J or
kg·m2
s2
4 The duration of an object’s
motion. Time Scalar s
5 The force exerted over an area. Pressure Vector Pa or kg
m·s2
6 The force exerted over time. Impulse Vector N·s or kg·m
s
7 The pull exerted on a string or
rope. Tension Vector N or
kg·m
s2
8 The rate at which an object’s
velocity changes. Acceleration Vector
m
s2
9 The rate at which momentum
changes. Force Vector N or
kg·m
s2
10 The rate of change of an
object’s position. Velocity Vector
m
s
11 The stored energy of an object
due to its height.
Gravitational Potential
Energy Scalar J or
kg·m2
s2
12 The total length traveled by an
object. Distance Scalar m
2 Kinematics: Motion in
One-Dimension
1. How long would it take a car, starting from rest
and accelerating uniformly in a straight line at 5
m/s2, to cover a distance of 200 m?
a) 9.0 s c) 12.0 s
b) 10.5 s d) 15.5 s
2. A 0.100 kg rubber ball is thrown downward from
the top of a building 30-m building with a speed of
4.0 m/s. How high above the ground is the ball
after 2.0 s?
a) 2.4 m d) 22.0 m
b) 8.0 m e) 27.6 m
c) 12.2 m
3. Which of the following statements are about
uniformly accelerated motion?
Select two answers.
a) If an object’s acceleration is constant then it
must move in a straight line.
b) If an object’s acceleration is zero, then it’s
speed must remain constant.
c) If an object’s speed remains constant, then its
acceleration must be zero.
d) If the object’s direction of motion is
changing then its acceleration is not zero.
4. On a horizontal number line, a fly is at the
coordinate +6. The fly then flies and lands at the
coordinate of –2. If the time traveled by the fly is
4 s, what is the fly’s velocity?
a) 2.0 units/s
b) 1.0 unit/s
c) –0.50 units/s
d) –1.0 unit/s
e) –2.0 units/s
5. A tennis ball is tossed vertically from the ground
with a speed of 30 m/s. With what speed will the
ball hit the ground?
a) 0 m/s d) 30 m/s
b) 10 m/s e) 40 m/s
c) 20 m/s
6. At a particular time, an object is moving with a
velocity of –20 m/s and an acceleration of 20 m/s2.
Which of the following is true about the object’s
motion?
a) It is not moving.
b) It is speeding up (accelerating).
c) It is slowing down (decelerating).
d) Its speed is not changing.
e) It is both speeding up and slowing down.
3 Kinematics in Two Dimensions
(Projectile Motion & Vectors)
7. A ball was pitched with a speed of 40 m/s at an
angle of 35° to the ground. What is the vertical
component of the velocity of the ball?
a) 23 m/s d) 49 m/s
b) 33 m/s e) 70 m/s
c) 40 m/s
Questions 8-10: A football is kicked with a horizontal
velocity of 20 m/s and a vertical velocity of 15 m/s.
8. What is the speed of the ball when it reaches its
peak?
a) 0 m/s d) 25 m/s
b) 15 m/s e) 35 m/s
c) 20 m/s
9. What is the speed of the ball when it returns to the
ground?
a) 0 m/s d) 25 m/s
b) 15 m/s e) 35 m/s
c) 20 m/s
10. How long does the ball travel in the air?
a) 1.5 s d) 5 s
b) 3 s e) 6 s
c) 4 s
* * * * * * * * * * * * * * * * * * * * * * * *
11. A stone is thrown horizontally with an initial
speed of 30 m/s from a bridge. Find the stone’s
total speed when it enters the water 4 seconds
later. (Ignore air resistance.)
a) 30 m/s c) 50 m/s
b) 40 m/s d) 60 m/s
12. A soccer ball, at rest on the ground, is kicked with
an initial velocity of 10 m/s at a launch angle of
30 . Calculate its total flight time, assuming that
air resistance is negligible.
a) 0.5 s c) 2 s
b) 1 s d) 4 s
13. Which one of the following statements is true
concerning the motion of an ideal projectile
launched at an angle of 45 to the horizontal?
a) The acceleration vector points opposite to the
velocity vector on the way up and in the same
direction as the velocity vector on the way
down.
b) The speed at the top of the trajectory is zero.
c) The object’s total speed remains
constant during the entire flight.
d) The vertical speed decreases on the way
up and increases on the way down.
4 Motion and Force: Dynamics
(Newton’s Three Laws of Motion)
14. A force of x newtons is applied to a crate on a
frictionless surface, and the crate accelerates at 2.0
m/s2. What force (in newtons) should be applied
for the crate to accelerate at 8.0 m/s2?
a) 0.5x
b) x
c) 2x
d) 3x
e) 4x
15. A 100-kg anchor is dropped in the water and falls
at a constant speed of 4.5 m/s. What is the force
of the resistance of the water encountered by the
anchor?
a) 10.2 N d) 530 N
b) 22.2 N e) 980 N
c) 450 N
16. A ball is released and rolls down a rough ramp
with an acceleration of 3.5 m/s2. Which of these
forces is NOT acting on the ball?
a) The weight of the ball.
b) The force of the ramp pushing on the
ball.
c) The force of friction between the ball
and the ramp.
d) The force of the push.
e) All of the above act on the ball.
17. A person standing on a horizontal floor feels two
forces: the downward pull of gravity and the
upward supporting force from the floor. These
two forces
a) have equal magnitudes and form an
action/reaction pair.
b) have equal magnitudes but do not form an
action/reaction pair.
c) have unequal magnitudes and form an
action/reaction pair.
d) have unequal magnitudes and do not form
an action/reaction pair.
18. A person who weighs 800 N steps onto a scale that
is on the floor of an elevator car. If the elevator
accelerates upward at a rate of 5 m/s2, what will
the scale read?
a) 400 N c) 1000 N
b) 800 N d) 1200 N
19. A frictionless inclined plane of length 20 m has a
maximum vertical height of 5 m. If an object of
mass 2 kg is placed on the plane, which of the
following best approximates the net force it feels?
a) 5 N c) 15 N
b) 10 N d) 20 N
20. A 20 N block is being pushed across a horizontal
table by an 18 N force. If the coefficient of kinetic
friction between the block and the table is 0.4, find
the acceleration of the block.
a) 0.5 m/s2 c) 5 m/s2
b) 1 m/s2 d) 7.5 m/s2
21. The coefficient of static friction between a box and
a ramp is 0.5. The ramp’s incline angle is 30. If
the box is placed at rest on the ramp, the box will
do which of the following?
a) Accelerate down the ramp.
b) Accelerate briefly down the ramp but then
slow down and stop.
c) Move with constant velocity down the ramp.
d) Not move.
22. If all of the forces acting on an object balance so
that the net force is zero, then
a) the object must be at rest.
b) the object’s speed will decrease.
c) the object’s direction of motion can
change, but not its speed.
d) None of the above will occur.
23. Assuming a frictionless, mass-less pulley,
determine the acceleration of the blocks once they
are released from rest.
m
M
a) m g
M + m
b) M g
m
c) (M + m) g
(M – m)
d) (M − m) g
(M + m)
24. A block of mass m is at rest on a frictionless,
horizontal table placed in a laboratory on the
surface of the Earth. An identical block is at rest
on a frictionless horizontal table placed on the
surface of the Moon. Let F be the net force
necessary to give the Earth – bound block an
acceleration of a across the table. Given that g
Moon is one-sixth of g Earth, the force necessary to
give the Moon – bound block the same
acceleration a across the table is
a) F/6 c) F
b) F/3 d) 6 F
25. A force F of strength 20 N acts on an object of
mass 3 kg as it moves a distance of 4 m. If F is
perpendicular to the 4 m displacement, the work it
does is equal to
a) 0 J c) 80 J
b) 60 J d) 600 J
26. Under the influence of a force, an object of mass 4
kg accelerates from 3 m/s to 6 m/s in 8 s. How
much work was done on the object during this
time?
a) 27 J c) 72 J
b) 54 J d) 96 J
5 Circular Motion and
Law of Gravitation
27. A 0.80-kg rubber stopper is connected to a string
and makes a circular path. Which of the following
requires the greatest tension on the string? (v =
speed of the rubber stopper;
r = radius of the circular path)
a) v = 6.0 m/s r = 0.40 m
b) v = 6.0 m/s r = 0.80 m
c) v = 9.0 m/s r = 0.60 m
d) v = 12.0 m/s r = 0.40 m
e) v = 12.0 m/s r = 0.80 m
28. A person’s weight is the same on Titan (one of
Saturn’s moons) as on Europa (one of Jupiter’s
moons). However, Europa’s radius is half that of
Titan’s. If the Europa has a mass of m kg, what is
Titan’s mass?
a) 0.25m d) 2m
b) 0.50m e) 4m
c) m
29. When a car is banking a curve (assuming circular
motion), which of the following is pointed in the
same direction as the friction between the tires and
the road?
I. Centripetal Acceleration
II. Centripetal Force
III. Instantaneous Velocity
a) I only.
b) II only.
c) III only.
d) I and II only.
e) I, II, and III.
(The Next Five Questions Are From the Chapter 5
Practice Test)
30. A ball is connected to a string and makes a circular
path. The tension on the string (which is the
centripetal force) is 6.0 N. If the radius remains
constant and the velocity doubles, what will be the
new tension on the string?
a) 1.5 N d) 12 N
b) 3.0 N e) 24 N
c) 6.0 N
31. A 0.020 kg rubber stopper is attached to one end of
a string that is passed through a plastic tube. At the
other end of the string weights are attached. A
student whirls the rubber stopper in a horizontal
circular path at constant speed, making ten
revolutions every 4 seconds. If the radius of the
circular path is 0.50 m, what is the centripetal
acceleration acting on the stopper?
a)0.16 m/s2 d) 12.5 m/s2
b) 2.5 m/s2 e) 123 m/s2
c) 5.0 m/s2
32. If an object moves with a frequency of 12
revolutions per minute, how many seconds does it
take to make three revolutions?
a) 9 d) 24
b) 12 e) 36
c) 15
33. A 500 g toy train (as shown below) completes 10
laps of its circular track in 1 minute and 40
seconds. If the diameter of the track is 1 meter,
find the train’s
(a) centripetal acceleration, ac = 0.197 m/s2
(b) centripetal force, Fc = 0.099 N
(c) period, T = 10 s
(d) frequency, f = 0.1 Hz
34. Alan makes 38 complete revolutions on the
playground “Round-A-Bout” in 30 seconds. If the
radius of the Round-A-Bout is 1meter, determine
the
(a) Period of the motion, T = 0.789 s
(b) Frequency of the motion, f = 1.27 Hz
(c) Linear speed at which Alan revolves = 7.96 m/s
(d) Centripetal force on 40 kg Alan = 2530 N
6 Work and Energy
35. A 2.5-kg box is pushed across a surface with a
force of 2.0 N at a constant speed of 1.5 m/s. What
is the coefficient of kinetic friction between the
box and the surface?
a\ 0.080
b) 0.53
c) 0.80
d) 1.3
e) 1.9
36. A box of mass m slides down a frictionless
inclined plane of length L and vertical height h.
What is the change in its gravitational potential
energy?
a) − m g L c) − m g L/h
b) − m g h d) − m g h/L
37. While a person lifts a book of mass 2 kg from the
floor to a tabletop, 1.5 m above the floor, how
much work does the gravitational force do on the
book?
a) − 30 J c) 0 J
b) − 15 J d) 15 J
38. A block of mass 3.5 kg slides down a frictionless
inclined plane of length 6.4 m that makes an angle
of 30 with the horizontal. If the block is released
from rest at the top of the incline, what is its speed
at the bottom?
a) 5.0 m/s c) 8.0 m/s
b) 6.4 m/s d) 10 m/s
39. An astronaut drops a rock from the top of a crater
on the Moon. When the rock is halfway down to
the bottom of the crater, its speed is what fraction
of its final impact speed?
a) 1/4 c) 1/2
b) 1/2√2 d) 1/√2
40. A force of 200 N is required to keep an object
sliding at a constant speed of 2 m/s across a rough
floor. How much power is being expended to
maintain this motion?
a) 50 W c) 200 W
b) 100 W d) 400 W
41. A 2.5-kg box is pushed across a surface with a
force of 2.0 N at a constant speed of 1.5 m/s. What
is the coefficient of kinetic friction between the
box and the surface?
a) 0.080 d) 1.3
b) 0.53 e) 1.9
c) 0.80
42. Two identical cars (they have the same mass) are
driving on a freeway. One is traveling at 72 mph,
while the other one is traveling at 32 mph. What
is the ratio of the kinetic energy of the first car to
that of the second car?
a) 0.444 d) 2.25
b) 0.667 e) 5.0
c) 1.50
43. A delivery man carries a 5.0-kg box up a flight of
stairs 4.0 m above the ground. How much work
was done on the box by the man?
a) 0 J d) 98 J
b) 20 J e) 196 J
c) 49 J
44. A 57-g tennis ball was dropped from a height of
2.0 m. If it bounces back up to a height of 1.8 m,
how much energy was transferred when it hit the
ground?
a) 0 J d) 0.56 J
b) 0.011 J e) 1.0 J
c) 0.11 J
45. A pulley system lifts a 20-kg box 1.5 m into the
air. If 6.0 m of rope was pulled, what was the
tension on the string?
a) 5.0 N d) 196 N
b) 49 N e) 784 N
c) 80 N
7 Linear Momentum
Chapter 7 will have the greatest number of questions
since no test on Chapter 7 will be given before the
Midterm and so more practice is needed.
46. A hammer that hits a nail with a 150 N force
delivers an impulse of 0.75 N • s. How long did
the hammer make contact with the nail?
a) 0.0050 s d) 2.0 s
b) 0.020 s e) 200 s
c) 0.50 s
47. A force of 15 N was applied to a 5.0 kg ball so it
accelerates from 2.0 m/s to 8.0 m/s. How long
was this force applied?
a) 0.50 s d) 3.0 s
b) 2.0 s e) 6.0 s
c) 2.5 s
48. Ball A has a mass of 2.0 kg and is rolling across a
smooth surface. If Ball B is moving twice as fast
as Ball A, but has the same momentum, what is
Ball B’s mass?
a) 0.50 kg
b) 1.0 kg
c) 2.0 kg
d) 4.0 kg
e) Not enough information to determine.
49. A car of a train moves at a constant speed of 20 m/s
toward another identical car that is at rest. If the
two cars lock together when they collide, what will
be the speed that the two cars will move?
a) 0 m/s d) 30 m/s
b) 10 m/s e) 40 m/s
c) 20 m/s
50. A boy delivers a 0.72 N·s impulse on a 1.2-kg toy
train by pushing it for 5.0 s. If the toy train’s initial
velocity was 0.60 m/s, what’s the final momentum
of the train?
a) 0.60 N·s d) 1.44 N·s
b) 0.72 N·s e) 3.00 N·s
c) 1.20 N·s
51. An object rolling at a constant speed has a
momentum of 60 N • s. If the mass of the object is
doubled and the speed is tripled, what is the new
momentum?
a) 10 N • s d) 120 N • s
b) 30 N • s e) 360 N • s
c) 60 N • s
52. When a porcelain bowl is dropped 1 m on a
padded mat, it does not break. Which of these
is smaller compared to dropping it on the hard
ground?
I. The impulse.
II. The speed of the bowl.
III. The force of impact.
a) I only.
b) II only.
c) III only.
d) I and III only.
e) I, II, and III.
53. Runner A is moving at 3 m/s and Runner B is
moving at 6 m/s. If the two runners have the
same momentum, and Runner A has a mass of
x kg, what is the mass of Runner B in kg?
a) 0.33x
b) 0.50x
c) 2.0x
d) 3.0x
e) 6.0x
54. A particle is moving at a constant speed in a
circular path. The momentum vector is
pointing:
a) Curved along the path of the circle.
b) Inward, toward the center of the circle.
c) Outward, away from the center of the circle.
d) Tangent to the circle, in the direction of
the motion.
e) Tangent to the circle opposite to the
direction of motion.
55. The units for impulse are:
a) kg • m • s
b) kg • m • s–1
c) kg • m • s–2
d) kg • m–1 • s–2
e) kg • m2 • s–2
56. When a force of 30 N is applied to each of the
following, which will require the most time to
stop?
a) m = 30 kg v = 12 m/s
b) m = 30 kg v = 24 m/s
c) m = 45 kg v = 18 m/s
d) m = 60 kg v = 12 m/s
e) m = 60 kg v = 24 m/s
57. A force is applied to a block over a period of 6
seconds. The graph is shown below. What is
the impulse from t = 0 s to t = 3 s?
a) 3.3 N • s d) 30 N • s
b) 10 N • s e) 45 N • s
c) 15 N • s
58. A 20-N force is applied for 3 s against a 15-kg
ball moving at 5 m/s to slow it down. What is
the final speed of the ball?
a) 0.50 m/s d) 2.0 m/s
b) 1.0 m/s e) 2.5 m/s
c) 1.5 m/s
Fo
rce
(N)
Time (s)
5
10
15
0 0 2 4 6
59. A 5.0-kg ball is dropped from the top of a
balcony for 3.0 s. Approximately what is the
impulse on the ball over this time?
a) 15 N • s
b) 30 N • s
c) 50 N • s
d) 75 N • s
e) 150 N • s
60. Which of the following is true for an inelastic
collision?
I. After the collision, the collided objects
move together as one object.
II. There is a loss of energy for the system
during the collision.
III. There is a loss of momentum for the
system during the collision.
a) I only.
b) II only.
c) III only.
d) I and II only.
e) I, II, and III.
61. Ball A, which has a mass of 1.0 kg, moves with
a velocity of +1.5 m/s. It collides elastically
with Ball B, which has a mass of 0.50 kg and is
at rest. If Ball A comes to a rest after the
collision, what is the final velocity of Ball B?
a) 0 m/s
b) 0.75 m/s
c) 1.0 m/s
d) 2.0 m/s
e) 3.0 m/s
62. Jon, who has a mass of 60 kg, runs 1.0 m/s
eastward and collides with Peter, who has a
mass of 80 kg and is at rest. After the inelastic
collision,
a) Both Jon and Peter will move eastward at
a speed less than 1.0 m/s.
b) Both Jon and Peter will move eastward at a
speed of 1.0 m/s.
c) Both Jon and Peter will move eastward at a
speed greater than 1.0 m/s.
d) Jon will stop moving, while Peter will move
eastward at a speed less than 1.0 m/s.
e) Jon will fall westward, while Peter will
move eastward at 1.0 m/s.
63. A 0.050 kg bullet is shot from a 5.0 kg rifle. If
the bullet travels at 80 m/s, what is the recoil
velocity of the rifle?
a) 0.0030 m/s
b) 0.010 m/s
c) 0.060 m/s
d) 0.80 m/s
e) 10 m/s
64. Ball A has a mass of 2.0 kg and Ball B has a
mass of 4.0 kg. When the two balls collide
elastically, which of the following is NOT true?
a) The force of Ball A hitting Ball B is equal to
in magnitude as the force of the Ball B
hitting Ball A.
b) The impulse of the collision is zero.
c) The net force on the system is zero.
d) The sum of the velocities of the balls
before the collision is equal to that after
the collision.
e) The total momentum of both balls before the
collision is equal to that after the collision.
The Midterm Exam will not have
any Free Response Questions,
however, solving these Free
Response Questions that follow
will be helpful to your studying!
Free Response
Please show all work neatly with units for
computational problems Answers should be
recorded with the appropriate number of
significant figures, the correct direction (+ or –,
if applicable), and units. Any responses
without adequate work would not be given
full credit for a Unit Exam.
Free Response Answers
Please show all work neatly for computational
problems (I.E.S.A.). Answers should be
recorded with the appropriate number of
significant figures, the correct direction (+ or –,
if applicable), and units. Any responses
without adequate work would not be given
full credit.
Chapter 2: Motion in 1D
1. An object is moving in along a straight line
according to velocity vs. time graph below.
Every interval along the x-axis represents 1
s, and every interval along the y-axis
represents 1 m/s.
Describe the object’s motion from t = 0 s to
t = 6 s. (2 points)
From t = 0 to t = 2, the object is moving at
a constant speed of 3 m/s.
From t = 2 to t = 6, the object is moving
with constant acceleration from 3 m/s to 6
m/s.
2. A foam ball is launched from the ground
straight up with a velocity of 40 m/s. What
is the ball’s velocity after 6.2 s? (4 points)
t = 6.2 s v = v0 +
at = (40 m/s) + (–9.8 m/s2)(6.2 s) = –20.8
m/s
v0 = 40 m/s
v = ?
a = –9.8 m/s2
Chapter 3: Motion in 2D
3. A cannon ball is fired with a horizontal
velocity of 6.0 m/s and a vertical velocity of
2.5 m/s.
(a) What is the initial velocity with which
the cannonball was fired? (2 points)
vx = 6.0 m/s v =
vx2 + vy
2 = (6.0 m/s)2 + (2.5 m/s)2 = 6.5
m/s
vy = 2.5 m/s
v = ?
(b) After how many seconds will the ball
return to the ground? (4 points)
t = ?
dy = v0yt + ½ at2
dy = 0 m (0 m) =
(2.5 m/s)(t) + ½ (–9.8 m/s2)(t2)
v0y = 2.5 m/s t = 0.51
s
a = –9.8 m/s2
velo
city
time
Chapter 4: Forces
4. In the setup shown, box A has a mass of
0.30 kg and box B has a mass of 0.025 kg.
Assume no friction.
(a) Draw the free body diagram for this
system. (2 points)
(b) What is the acceleration with which this
system moves? (4 points)
mA = 0.30 kg
Fnet =
msys asys
mB = 0.025 kg
WB – T
+ T = (mA + mB)(asys)
WA = mAg = (0.30 kg)(9.8 m/s2) = 2.94 N
(0.245 N) = (0.30 kg + 0.025 kg)(asys)
WB = mBg = (0.025 kg)(9.8 m/s2) = 0.245 N
a = 0.754 m/s2
Chapter 5: Circular Motion
5. A 0.150-kg mass is tied to a 0.60-m string
and swung to make a circular orbit.
(a) If the tension on the string is 20.0 N,
what is the speed with which the mass
travels? (4 points)
FC = 20.0 N FC =
mv2
r
m = 0.150 kg (20.0
N) = (0.150 kg)v2
(0.60 m)
v = ?
v = 8.9 m/s
r = 0.60 m
(b) Draw the vector that represents the path
of the mass if the string was let go. (2
points)
A
B
N
WA
WB
T
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Chapter 6: Energy
6. A 0.400-kg soccer ball was kicked from the
ground with an initial speed of 32.5 m/s.
(a) Find the maximum height if it is moving
at 12.5 m/s at that point. (4 points)
Before After
PEbefore + KEbefore = PEafter +
KEafter
m = 0.400 kg m = 0.400 kg
1
2 mv2 = mgh
h = 0 m h = ?
1
2 (0.400 kg)(32.5 m/s)2 =
(0.400 kg)(9.8 m/s2)h
v = 32.5 m/s v = 0 m/s
h = 53.9 m
(b) Why is the ball traveling slower at the
height of its path? Explain briefly using
energy arguments.
(2 points)
At the height of the path, all the kinetic
energy at the beginning has been
converted to potential energy. With less
kinetic energy, it travels at a slower
speed.
Chapter 7: Momentum
7. A 1500-kg car traveling at 15 m/s collides
inelastically with a 3500-kg pick-up truck at
rest.
(a) With what speed to the vehicles move
after the collision? (4 points)
Before After
pbefore = pafter
m1 = 1500 kg m1 = 1500 kg
m1v1 + m2v2 = (m1 + m2)v
v1 = 15 m/s m2 = 3500 kg
(1500 kg)(15 m/s) + (3500 kg)(0 m/s) =
(1500 kg + 3500 kg)v
m2 = 3500 kg V = ?
v = 4.5 m/s
v2 = 0 m/s
(b) If time of impact of the collision was 2.0
s, what force was experienced by the
pick-up truck? (4 points)
m = 3500 kg J = ∆p
= m(v – v0) = Ft
v0 = 0 m/s (3500
kg)(4.5 m/s – 0 m/s) = (F)(2.0 s)
v = 4.5 m/s F =
7875 N
F = ?
t = 2.0 s