AP Physics B 2009-2010 First Semester Final Exam
Part I: Multiple-Choice Section
Ignore air resistance unless stated otherwise.
1. When is the average velocity
of an object equal to the instantaneous velocity of the object?
A) always
B) never
C) only when the velocity is constant
D) only when the velocity is increasing at a constant rate
Answer: C
2. Given that a car is
traveling to the East (+x direction) and it begins to slow down as it
approaches a traffic light.
Make a statement concerning its acceleration.
A) The car is decelerating, and its acceleration is positive.
B) The car is decelerating, and its acceleration is negative.
C) The acceleration is zero.
D) A statement cannot be made using the information given.
Answer: B
3. An object is moving with a
constant velocity. Which of the
following is true concerning its acceleration?
A) The acceleration must be constantly increasing.
B) The acceleration must be constantly decreasing.
C) The acceleration must be a constant non-zero value.
D) The acceleration must be equal to zero.
Answer: D
4. An object is released from
rest and falls in the absence of friction. Which of the following statements
is true concerning its motion?
A) Its acceleration is constant.
B) Its velocity is constant.
C) Neither its acceleration nor its velocity is constant.
D) Both its acceleration and its velocity are constant.
Answer: A
5. What does the area under a
curve in an acceleration versus time graph give?
A) acceleration.
B) velocity.
C) displacement.
D) position.
Answer: B
6. Which of the following
operations will not change a vector?
A) Translate it parallel to itself.
B) Multiply it by a constant factor.
C) Add a constant vector to it.
D) Rotate it.
Answer: A
7. If you ignore air
resistance, the horizontal component of a projectile's velocity
A) is zero.
B) remains constant.
C) continuously increases.
D) continuously decreases.
Answer: B
Note:
8. Given that a ball is kicked
with a velocity of 25 m/s at an angle of 45° above the horizontal.
What is the vertical component of its acceleration as it travels
along its trajectory?
A) 9.80 m/s2 downward
B) (9.80 m/s2)
× sin (45°) downward
C) (9.80 m/s2)
× sin (45°) upward
D) (9.80 m/s2)
upward
Answer: A
9. A rock is thrown
horizontally from the top of a building at the same instant a ball is
dropped vertically. Which
object is traveling faster when it hits the level ground below?
A) It is impossible to tell from the information given.
B) the rock
C) the ball
D) Neither, since both are traveling at the same speed.
Answer: B
Note: The thrown rock has both a vertical and a horizontal component of velocity. The ball has only 1.
10. A bomber pilot drops a bomb
from an airplane that is flying horizontally at a constant speed.
Neglecting air resistance, when the bomb hits the ground the
horizontal location of the plane will
A) be behind the bomb.
B) be over the bomb.
C) be in front of the bomb.
D) depend on the speed of the plane when the bomb was released.
Answer: B
11. Motorists should always
buckle up. This is best explained by which one of Newton's laws?
A) the first law
B) the second law
C) the third law
D) the law of gravitation
Answer: A
12. In the absence of an
external force, a moving object will
A) stop immediately.
B) slow down and eventually come to a stop.
C) go faster and faster.
D) move with constant velocity.
Answer: D
13. A net force accelerates a
mass m with an acceleration a.
If the same net force is applied to mass 2m, then the acceleration will be
A) 4a.
B) 2a.
C) a/2.
D) a/4.
Answer: C
14. Two cars collide head-on.
At every moment during the collision, the magnitude of the force the
first car exerts on the second is exactly equal to the magnitude of the
force the second car exerts on the first.
This is an example of
A) Newton's first law.
B) Newton's second law.
C) Newton's third law.
D) Newton's law of gravitation.
Answer: C
15. A 30-ton truck collides
with a 2000-lb car and causes a lot of damage to the car.
Since a lot of damage is done on the car
A) the force on the truck is greater then the force on the car.
B) the force on the truck is equal to the force on the car.
C) the force on the truck is smaller than the force on the car.
D) the truck did not slow down during the collision.
Answer: B
16. Given that an object of
mass m sits on a flat table.
The Earth pulls on this object with force mg, which we will call the action
force. What is the reaction
force?
A) The table pushing up on the object with force mg.
B) The object pushing down on the table with force mg.
C) The table pushing down on the floor with force mg.
D) The object pulling upward on the Earth with force mg.
Answer: D
17. The acceleration due to
gravity is lower on the Moon than on Earth.
Which of the following is true about the mass and weight of an
astronaut on the Moon's surface, compared to Earth?
A) Mass is less, weight is same.
B) Mass is same, weight is less.
C) Both mass and weight are less.
D) Both mass and weight are the same.
Answer: B
18. Assume the presence of air
resistance for this problem. A hammer and a feather fall to the earth at
their respective terminal velocities.
Which object experiences the greater force of air friction?
A) the feather
B) the hammer
C) Neither, both experience the same amount of air friction.
D) It cannot be determined because there is not enough information given.
Answer: B
NOTE: Ffr = mkFN FN = mg for both g is same for both FN is directly proportional to m, which is greater for the hammer
19. Is it possible for an
object moving with a constant speed to accelerate?
Explain.
A) No, if the speed is constant then the acceleration is equal to zero.
B) No, an object can accelerate only if there is a net force acting on it.
C) Yes, although the speed is constant, the direction of the velocity can be
changing.
D) Yes, if an object is moving it can experience acceleration
Answer: C
20. A
particle is moving with constant
speed such that its acceleration of constant magnitude is always
perpendicular to its velocity.
A) It is moving in a straight line.
B) It is moving in a circle.
C) It is moving in a parabola.
D) None of the above is definitely true all of the time.
Answer: B
21. Which of the following
forces is needed to make an object move in a circle?
A) kinetic friction
B) static friction
C) centripetal force
D) weight
Answer: C
22. A car goes around a curve
of radius r at a constant speed v.
It then goes around the same curve at half the original speed.
What is the centripetal force on the car as it goes around the curve
the second time, as compared to the first time it went around the curve?
A) twice as big
B) four times as big
C) half as big
D) one-fourth as big
Answer: D
23. Two objects attract each
other gravitationally. If the
distance between their centers is cut in half, the gravitational force
A) is cut to one fourth.
B) is cut in half.
C) doubles.
D) quadruples
Answer: D
24. Can work be done on a
system if there is no motion?
A) Yes, if an outside force is provided.
B) Yes, since motion is only relative.
C) No, since a system which is not moving has no energy.
D) No, because of the way work is defined.
Answer: D
25. If you walk 5.0 m
horizontally forward at a constant velocity carrying a 10-N object, the
amount of work you do is
A) more than 50 J.
B) equal to 50 J.
C) less than 50 J, but more than 0 J.
D) zero.
Answer: D
26. If the net work done on an
object is zero, then the object's kinetic energy
A) decreases.
B) remains the same.
C) increases.
D) is zero.
Answer: B
27. A brick is moving at a
speed of 3 m/s and a pebble is moving at a speed of 5 m/s.
If both objects have the same kinetic energy, what is the ratio of
the brick's mass to the rock's mass?
A) 25 to 9
B) 5 to 3
C) 12.5 to 4.5
D) 3 to 5
Answer: A
28. Consider two masses m1 and
m2 at
the top of two frictionless inclined planes.
Both masses start from rest at the same height.
However, the plane on which m1 sits
is at an angle of 30° with the horizontal, while the plane on which m2 sits
is at 60°. If the masses are
released, which is going faster at the bottom of its plane?
A) m1
B) m2
C) They both are going the same speed.
D) cannot be determined without knowing the masses
Answer: C
29. When a cannon fires a
cannonball, the cannon will recoil backward because the
A) energy of the cannonball and cannon is conserved.
B) momentum of the cannonball and cannon is conserved.
C) energy of the cannon is greater than the energy of the cannonball.
D) momentum of the cannon is greater than the energy of the cannonball.
Answer: B
30. If you pitch a baseball
with twice the kinetic energy you gave it in the previous pitch, the
magnitude of its momentum is
A) the same.
B) 1.41 times as much.
C) doubled.
D) 4 times as much.
Answer: B
Note: (KE)2 = 2(KE)1 1/2mv22 = mv12 mass did not change, so 1/2v22 = v12 ð v2 = (2)1/2v1 = 1.41v1
so, since momentum = mv if v increases by 1.4 then the momentum increases by 1.41
31. Which of the following is
an accurate statement?
A) The momentum of a projectile is constant.
B) The momentum of a moving object is constant.
C) If an object is acted on by a non-zero net external force, its momentum
will not remain constant.
D) If the kinetic energy of an object is doubled, its momentum will also
double.
Answer: C
32. A 3.0-kg object moves to
the right at 4.0 m/s. It
collides head-on with a 6.0-kg object moving to the left at 2.0 m/s.
Which statement is correct?
A) The total momentum both before and after the collision is 24 kg∙ m/s.
B) The total momentum before the collision is 24 kg∙m/s, and after the
collision is 0 kg∙m/s.
C) The total momentum both before and after the collision is zero.
D) None of the above is true.
Answer: C
33. In an inelastic collision,
if the momentum is conserved, then which of the following statements is true
about kinetic energy?
A) Kinetic energy is also conserved.
B) Kinetic energy is gained.
C) Kinetic energy is lost.
D) none of the above
Answer: C
34.
A boy and a girl are riding on a
merry-go-round which is turning at a constant rate.
The boy is near the outer edge, and the girl is closer to the center.
Who has the greater angular displacement?
A) the boy
B) the girl
C) Both have the same non-zero angular displacement.
D) Both have zero angular displacement.
Answer: C
35. Consider a rigid body that
is rotating. Which of the
following is an accurate statement?
A) Its center of rotation is its center of gravity.
B) All points on the body are moving with the same angular velocity.
C) All points on the body are moving with the same linear velocity.
D) Its center of rotation is at rest, i.e., not moving.
Answer: B
36. Two forces are applied to a
doorknob, perpendicular to the door.
The first force is twice as large as the second force.
The ratio of the torque of the first to the torque of the second is
A) 1/4.
B) 1/2.
C) 2.
D) 4.
Answer: C
37. Two uniform solid spheres
have the same mass, but one has twice the radius of the other.
The ratio of the larger sphere's moment of inertia to that of the
smaller sphere is
A) 4/5.
B) 8/5.
C) 2.
D) 4.
Answer: D
38. An ice skater performs a
pirouette (a fast spin) by pulling in his outstretched arms close to his
body. What happens to his
angular momentum about the axis of rotation?
A) It does not change.
B) It increases.
C) It decreases.
D) It changes, but it is impossible to tell which way.
Answer: A
39. A book weighs 6 N.
When held at rest above your head the net force on the book is
A) 0 N.
B) 6 N.
C) 9.8 N.
D) -6 N.
Answer: A
40. A heavy boy and a light
girl are balanced on a massless seesaw.
If they both move forward so that they are one-half their original
distance from the pivot point, what will happen to the seesaw?
A) The side the boy is sitting on will tilt downward.
B) The side the girl is sitting on will tilt downward.
C) Nothing, the seesaw will still be balanced.
D) It is impossible to say without knowing the masses and the distances.
Answer: C
41. A sphere hanging freely
from a cord is in
A) stable equilibrium.
B) unstable equilibrium.
C) neutral equilibrium.
D) positive equilibrium.
Answer: A
42. Consider two identical
bricks, each of dimensions 20.0 cm × 10.0 cm × 6.0 cm.
One is stacked on the other, and the combination is then placed so
that they project out over the edge of a table.
What is the maximum distance that the end of the top brick can extend
beyond the table edge without toppling?
A) 7.5 cm
B) 10 cm
C) 12.5 cm
D) 15 cm
Answer: D
43. Density is
A) proportional to both mass and volume.
B) proportional to mass and inversely proportional to volume.
C) inversely proportional to mass and proportional to volume.
D) inversely proportional to both mass and volume.
Answer: B
44. Consider three drinking
glasses. All three have the
same area base, and all three are filled to the same depth with water.
Glass A is cylindrical.
Glass B is wider at the top than at the bottom, and so holds more water than
A. Glass C is narrower at the
top than at the bottom, and so holds less water than A.
Which glass has the greatest liquid pressure at the bottom?
A) Glass A
B) Glass B
C) Glass C
D) All three have equal pressure.
Answer: D
45. 50 cm3 of
wood is floating on water, and 50 cm3 of
iron is totally submerged.
Which has the greater buoyant force on it?
A) the wood
B) the iron
C) Both have the same buoyant force.
D) cannot be determined without knowing their densities
Answer: B
46. As a rock sinks deeper and
deeper into water of constant density, what happens to the buoyant force on
it?
A) It increases.
B) It remains constant.
C) It decreases.
D) It may increase or decrease, depending on the shape of the rock.
Answer: B
47. A piece of iron rests on
top of a piece of wood floating in a bathtub. If the iron is removed from
the wood, what happens to the water level in the tub?
A) It goes up.
B) It goes down.
C) It does not change.
D) impossible to determine from the information given
Answer: B
48. A piece of wood is floating
in a bathtub. A second piece of
wood sits on top of the first piece, and does not touch the water.
If the top piece is taken off and placed in the water, what happens
to the water level in the tub?
A) It goes up.
B) It goes down.
C) It does not change.
D) cannot be determined from the information given
Answer: C
49. An ideal fluid flows at 12
m/s in a horizontal pipe. If the pipe widens to twice its original radius,
what is the flow speed in the wider section?
A) 12 m/s
B) 6.0 m/s
C) 4.0 m/s
D) 3.0 m/s
Answer: D
50. As the speed of a moving
fluid increases, the pressure in the fluid
A) increases.
B) remains constant.
C) decreases.
D) may increase or decrease, depending on the viscosity.
Answer: C
51. Two horizontal pipes are
the same length, but pipe B has twice the diameter of pipe A.
Water undergoes viscous flow in both pipes, subject to the same
pressure difference across the lengths of the pipes.
If the flow rate in pipe A is Q, what is the flow rate in pipe B?
A) 2Q
B) 4Q
C) 8Q
D) 16Q
Answer: D
52. Two displacement vectors
have magnitudes of 5.0 m and 7.0 m, respectively.
When these two vectors are added, the magnitude of the sum
A) is 2.0 m.
B) could be as small as 2.0 m, or as large as 12 m.
C) is 12 m.
D) is larger than 12 m.
Answer: B
minimum occurs when they are in opposite directions = 2
53. Does the centripetal force
acting on an object do work on the object?
A) Yes, since a force acts and the object moves, and work is force times
distance.
B) Yes, since it takes energy to turn an object.
C) No, because the object has constant speed.
D) No, because the force and the displacement of the object are
perpendicular.
Answer: D
54. A ball falls from the top
of a building, through the air (air friction is present), to the ground
below. How does the kinetic
energy (K) just before striking the ground compare to the potential energy
(U) at the top of the building?
A) K is equal to U.
B) K is greater than U.
C) K is less than U.
D) It is impossible to tell.
Answer: C
55. The area under the curve,
on a Force versus position (F vs. x) graph, represents
A) work.
B) kinetic energy.
C) power.
D) potential energy.
Answer: A
56. Action-reaction forces
A) sometimes act on the same object.
B) always act on the same object.
C) may be at right angles.
D) always act on different objects.
Answer: D
57. In an elastic collision, if
the momentum is conserved, then which of the following statements is true
about kinetic energy?
A) Kinetic energy is also conserved.
B) Kinetic energy is gained.
C) Kinetic energy is lost.
D) none of the above
Answer: A
58. A 3.0-kg object moves to
the right at 4.0 m/s. It
collides in a perfectly inelastic collision with a 6.0 kg object moving to
the left at 2.0 m/s. What is
the total kinetic energy after the collision?
A) 72 J
B) 36 J
C) 24 J
D) 0 J
Answer: D
59. Which one of the following
is associated with the law of conservation of energy in fluids?
A) Archimedes' principle
B) Bernoulli's principle
C) Pascal's principle
D) equation of continuity
Answer: B
60. Winter break begins in
A) January
B) March
C) December
D) June
E) July
Answer: C
Part II: Free-Response Section
Problem 1
|
A block of mass m1 is on a smooth horizontal surface, connected by a thin cord that
passes over a pulley to a second block of mass m2, which
hangs vertically.
A picture of the arrangement is shown on the right. |
|
a. Draw a free-body diagram for each block, showing all forces. Indicate the
directions chosen
as positive.
b. Apply Newton’s second law to find formulas for the acceleration of the system. Ignore friction and the masses of the pulley and cord. Note that
a numerical solution is not required for this problem.
For block 1, since there is no motion in the vertical direction, we have Fn1
= m1g.
We can write Newton’s 2nd law for the
x direction as follows
SF1x
= FT = m1a1x
For block 2, we only need to consider vertical forces:
SF2y
= m2g - FT = m2a2y
Since the two blocks are connected, the magnitudes of their accelerations
will be the same, and so a1x = a2y = a.
Combine the two force equations from above, and solve for
a by substitution.
FT = m1a
m2g - FT = m2a
ð
m2g - m1a
= m2a
m1a + m2a = m2g
ð
a = gm2/(m1 + m2)
Problem 2
As shown above, a 1 kg wooden block is on a level board and held against a
spring of force constant - also called the spring stiffness constant - of
30.0 N/m. The spring has been compressed 0.200 m from its unstretched
length. The block is released and propelled horizontaly across the board.
Assume that friction between the block and board is negligible.
Determine the velocity of the block just as it leaves the spring.
DPEspring
=
DKEblock
1/2kx2 = 1/2 mv2
ð
kx2 = mv2
ð
v = (k/m)1/2x
v = (30.0 N/m)/1.0 kg)1/2(0.200 m) = 1.10 m/s
Problem 3
What fraction of a piece of aluminum will be submerged when it floats in
mercury? Assume that the
density of aluminum is 2.7x103 kg/m3 and the density
of mercury is 13.6 x103 kg/m3.
If the aluminum is floating, then the net force on it is zero.
The buoyant force on the aluminum must be equal to its weight.
The buoyant force is equal to the weight of the mercury displaced by
the submerged aluminum.
Fbuoyant = malg
ð
rHggVsubmerged
=
rAlgVtotal
Vsubmerged/Vtotal =
rAl/rHg
= 2.7x103 kg/m3/13.6 x103 kg/m3
%
by inspection, we can see that 3/14 is approximately 20%
Part III: Extra Credit Section
1. Pictures and biographies of
some giants in chapter 13 are provided on my site. Identify the
following
(last name only). Place the
name below the picture. Some hints are provided
a. I am not George Washington. I am actually from France; a law is named
after me.
b. I am from Italy and I published many papers in physics and chemistry.
c. I am from Sweden and I founded an observatory there.
d. No, I am not Newton, but a law is also named after me. I am from Ireland.
2. Given an aluminum block that is 20.9 m long at 20.00 C. The coefficient for linear expansion of the material is 25.0 x 10-6/C0 . What would its
length be at 00 c?
∆L =
aL0∆t
=(25.0 x 10-6/C0 )x(20.0 m)x(-200 c) = -.01
m
Subtract this from the initial length
20.9 - .01 m
3. How many moles are in Y
grams of a substance whose molecular mass is Z unified atomic mass units
(u)
number of moles = mass in grams/molecular mass (g/mole) = Y/Z
