Download Physics C Test January 2011

NJSL Physics C January Exam 2011
1. Determine the change in the kinetic energy of a small box attached to a non-elastic spring that stretches
from x = 0.2 m to x = 0.3 m while applying a force F = bx3 on the box. Here b = 104 N/m3 is the force constant
for this spring and x is the amount the spring is stretched from its unstretched length.
a . 16.25 J
b. 12.75 J
c. 9.5 J
d. 2.5 J
e. 0.25 J
2. In an action film a cannon is transported on an open train
platform moving straight at 40 m/s relative to the ground.
A cannon ball is shot at 50 m/s relative to the moving
platform at 143o to the direction of the train and above
horizontal as shown. What is the speed of the cannon ball
relative to the ground?
a. 40 m/s
b. 10 m/s c. 90 m/s d. 0 m/s e. 30 m/s
3. A small pebble falls off a ledge a height H above the ground. It takes to seconds to fall the first half of the
height H. Find the total time the pebble is in the air. Neglect air resistance.
a.
b.
c.
e. 2to
d.
4. An object of a mass m falls from rest subject to air resistance force directly proportional to the object’s
speed, F = - bv, where b is the proportionality constant in N/(m/s) and the negative sign indicates the
direction of the force opposite to the direction of the velocity. How long does it take this object to reach half
of its terminal speed?
a.
b.
c.
d.
e.
5. A relief package is dropped from an airplane flying horizontally at an altitude H and the speed v. How far is
the package from the plane when the package hits the ground? Assume that the plane continues to fly at
constant velocity.
a.
NJSL Phy C Jan 2011 Exam
b.
c.
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d. H
e. 2H
6. A small toy car slides through a loop without friction. The
toy car starts from rest at a height 4R above the bottom of
a loop of a radius R. What are the centripetal and the
tangential accelerations of the toy car at point C?
a. Centripetal = 2g, tangential = g
b. centripetal = 6g, tangential = g
c. centripetal = 3g, tangential = g,
d. centripetal = 6g, tangential =2g,
e. centripetal = g, tangential = 0
7. The change in the potential energy of an object moving from point a to point b is defined as
a. The work done by a conservative force in moving the object from point a to point b
b. …. Not defined
c. Opposite of the change in the kinetic energy of this object
d. The total work done by all forces in moving this object
e. Opposite of the work done by all the non-conservative forces
8. Two pucks undergo a head-on, elastic collision on an air table. Before collision, a lower-mass puck A is
moving to the right at 2 m/s and a heavier puck B is moving to the left at 1 m/s. What is the velocity of puck
A relative to puck B after collision?
a. Need to know the masses to answer the question
b. the pucks remain at rest after the head-on collision
c. after collision, velocity of puck A relative to puck B is 3 m/s to the left
d. after collision, velocity of puck A relative to puck B is 1 m/s to the left
e. after collision, velocity of puck A relative to puck B is 3 m/s to the right
For questions # 9, 10 use the following information:
A warehouse worker is attempting to move a box of a mass M resting on a flat floor
by pushing downward at an angle  below horizontal. The coefficient of static
friction between the box and floor is .
9. What happens to the magnitude of the normal force as the angle of the applied force increases?
a. The magnitude of the normal force increases
b. The magnitude of the normal force remains the same
c. The magnitude of the normal force decreases
d. Not enough information given
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10. At some maximum value of the angle even an infinitely strong force cannot start the box. What is this angle?
a.
b.
c.
d.
e. 45o
For question #11 refer to the potential diagram:
11. A particle starts out at ro with kinetic energy KE
= 3Uo. Where does this particle turn around?
a. There is no turning point with this amount
of KE since the particle leaves this system
b. The turning points are .25ro and 5.25ro
c. There is only one turning point, 0.25ro
d. The turning points are ro and 4ro
e. There is only one turning point, 4ro
12. When a fireworks rocket explodes high up in
above the ground, the center of mass of the
fragments
a. Slows down since kinetic energy has left the
system because of the explosion.
b. Speeds up since additional kinetic energy has been added to the system
c. Continues to fall as a projectile as it did before the explosion
d. Remains at rest at the top of the trajectory
e. Falls straight down under the action of gravity
13. The graph shows momentum of a particle as a function of time.
Which region corresponds to the time when the net force acting on
this particle is the greatest?
a. 1 b. 2 c. 3 d. 4
e. 1 and 3
14. A marble of a mass m moving at a speed vm to the right collides head-on, elastically with a bowling ball
moving to the left at a speed Vb. Assume that the mass of the bowling ball is much greater than the mass of
the marble and take the direction to right as positive. What is the velocity of the marble after collision?
a. -vm - 2Vb
b. -vm + 2Vb
c. -vm
d. -2vm
e. - Vb
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15. The coefficient of static friction between the table and the block M is s. The
three ropes are attached to the ring in the center as shown. The slanted rope
is attached to the wall and makes an angle  with the vertical. The system
remains in equilibrium. What is the friction force acting on block M?
a.
b.
c.
d.
e. 0
16. A perfectly elastic spring is attached to the ceiling and a mass m is hanging from the spring. The mass is in
equilibrium when the spring is stretched a distance xo. The mass is carefully lifted
and held at rest in the position where the spring is neither stretched nor
compressed at all. The mass is then allowed to drop from rest. What is the
maximum extension of the spring from its unstretched length?
a. xo/2 b. xo c. 2xo d. 3xo e. 4xo
17. The ratio of weight to mass for an object is
a. Always equal to 1
b. depends on the mass of the object
c. depends on the location of the object
d. always the same but >1
e. depends on the season
18. Compute the work done by a force F = 2i – 3j +5k (where all constants are in Newtons) in moving a 5 kg
object from a point (0, 1m, 2m) to a point (5m, 2m, -4m).
a. 0
b. 16 J
c. -16 J
d. 23 J
e. – 23 J
For questions #19 and 20, use the following graph:
19. The graph shows the energy of a mass attached to an elastic
spring. Identify each curve:
a. 1 – Total Energy, 2 – kinetic energy, 3 – potential energy
b. 1 – Total Energy, 2 – potential energy, 3 – kinetic energy
c. 1 – Kinetic Energy, 2 – Potential energy, 3 – Total energy
d. 1 – Potential Energy, 2 – kinetic energy, 3 – total energy
e. None of these
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20. This graph illustrates the law of conservation of energy because it shows that
a. Kinetic energy is always opposite to potential energy
b. Potential and kinetic energy are both at a minimum when x =0
c. The change is kinetic energy is zero
d. The total energy remains the same for all positions (x)
e. Potential energy remains the same for all positions (x)
21. Three identical springs with identical force constants k are attached as shown. Determine the total distance
the mass is lowered when it is hanging from these springs.
a.
b.
c.
d.
e.
22. A plane is flying horizontally. At the time the plane is directly overhead you hear the sound from the plane as
coming from behind the plane at 30o to the vertical (as shown). The speed of the plane is
a. Equal to the speed of sound
b. equal to half the speed of sound
c. is equal to twice the speed of sound
d. cannot be determined
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23. A uniform square, 6 m on each side is missing one quarter part. Determine the x and
y coordinates of the center of mass of this square.
a . 0, 0 b. 0.56 m, 0.56 m c. 1.5 m, -1.5 m d. – 1 m, 1 m e. 0.50 m, -0.50 m
24. In a game of billiards, a q-ball traveling at a speed v collides elastically with a stationary 8-ball. After collision,
the 8-ball moves off at 37o to the original direction of the q-ball. Determine the velocity of the q-ball after
the collision.
a. 0.6v b. 0.8 v
c. 0.3 v d. 0.5 v
e. v
25. A frictionless ramp accelerates to the left at an acceleration a as shown. What is the ramp angle  if a block
remains at rest relative to the ramp?
a.
b.
c.
d. 30o
e. this is impossible without friction
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