Download Final Exam April 2008

CA M O S U N C O L L E G E
PHYSICS DEPARTMENT
Physics 115 Final Exam
April 2008
Instructor: Julie Alexander
Name _______________________
Show all of your work A single 8.5”X11” sheet of paper, handwritten on one side only is
permitted. Total marks 100: (34 for long answers and 3 each for 22 multiple choice)
1) An amusement park ride consists of a rotating circular platform 8.00 m in diameter from
which 10.0-kg seats are suspended at the end of 2.50-m massless chains as shown below.
When the system rotates, the chains make an angle  = 32.0 with the vertical.
(a) What is the speed of each seat? (4 marks)
Physics 115 Final Exam
2) A force


F  4x iˆ  3y ˆj N
2
acts on an object as the object moves in the x direction
from the origin to x = 8.00 m. Find the work done on the object by the force. (3 marks)
3) A toy cannon uses a spring to project a 5.60-g soft rubber ball. The spring is originally
compressed by 5.10 cm and has a force constant of 8.00 N/m. When it is fired, the ball
moves 15.0 cm through the horizontal barrel of the cannon, and there is a constant friction
force of 0.032 0 N between the barrel and the ball.
(a) With what speed does the ball leave the barrel of the cannon? (3 marks)
(b) What is the maximum speed of the ball while it is still in the barrel? (3 marks)
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4) A billiard ball moving at 5.40 m/s strikes a stationary ball of the same mass. After the
collision, the first ball moves at 4.33 m/s, at an angle of 30.0° with respect to the original line
of motion. Assuming an elastic collision (and ignoring friction and rotational motion), find the
struck ball's velocity after the collision.(4 marks)
5) A 10 000-N shark is supported by a cable attached to a 4.80-m rod that can pivot at the base.
a) Calculate the tension in the tie-rope between the rod and the wall if it is holding the
system in the position as shown below. (Neglect the weight of the rod.)
(3 marks)
b) Find the magnitude of the reaction force at the pivot. (3 marks)
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6) A particle moving along the x axis in simple harmonic motion starts from its equilibrium
position, the origin, at t = 0 and moves to the right. The amplitude of its motion is 2.00 cm
and the frequency is 1.50 Hz.
a)Determine the maximum speed and the earliest time (t > 0) at which the particle has this
speed, (3 marks)
(c) the total distance traveled between t = 0 and t = 1.00 s.(3 marks)
7) A charged cork ball of mass 1.20 g is suspended on a light string in the presence of a uniform
electric field as shown below. When E  3.00iˆ  5.00 ˆj  10 N / C , the ball is in
equilibrium at θ=40o.
a) Find the charge on the ball. (5 marks)
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Physics 115 Final Exam
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Answer sheet for Multiple Choice Problems (Please use lower case letters for your
answers)
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Physics 115 Final Exam.
Write your answers on the answer sheet provided with the long answers.
____
1. An object attached to the end of a string swings in a vertical circle (R = 1.2 m), as shown. At an
instant when  = 30, the speed of the object is 5.1 m/s and the tension in the string has a
magnitude of 20 N. What is the mass of the object?
a.
b.
c.
d.
e.
2.0 kg
1.5 kg
1.8 kg
1.2 kg
0.80 kg
____
2. A race car traveling at 100 m/s enters an unbanked turn of 400 m radius. The coefficient of
(static) friction between the tires and the track is 1.1. The track has both an inner and an outer
wall. Which statement is correct?
a. The race car will crash into the outer wall.
b. The race car will crash into the inner wall.
c. The car will stay in the center of the track.
d. The car will stay in the center of the track if the driver speeds up.
e. The car would stay in the center of the track if the radius were reduced to 200 m.
____
3. A 2.0-kg projectile moves from its initial position to a point that is displaced 20 m horizontally
and 15 m above its initial position. How much work is done by the gravitational force on the
projectile?
a. +0.29 kJ
b. 0.29 kJ
c. +30 J
d. 30 J
e. 50 J
____
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4. The only force acting on a 1.6-kg body as it moves along the x axis is given in the figure. If the
velocity of the body at x = 2.0 m is 5.0 m/s, what is its kinetic energy at x = 5.0 m?
a.
b.
c.
d.
e.
52 J
44 J
36 J
60 J
25 J
____
5. A 2.0-kg mass swings at the end of a light string (length = 3.0 m). Its speed at the lowest point on
its circular path is 6.0 m/s. What is its kinetic energy at an instant when the string makes an angle
of 50 with the vertical?
a. 21 J
b. 15 J
c. 28 J
d. 36 J
e. 23 J
____
6. A 1.0-kg block is released from rest at the top of a frictionless incline that makes an angle of 37
with the horizontal. An unknown distance down the incline from the point of release, there is a
spring with k = 200 N/m. It is observed that the mass is brought momentarily to rest after
compressing the spring 0.20 m. How far does the mass slide from the point of release until it is
brought momentarily to rest?
a. 0.98 m
b. 0.68 m
c. 0.82 m
d. 0.55 m
e. 0.20 m
7. A 1.5-kg playground ball is moving with a velocity of 3.0 m/s directed 30 below the horizontal
just before it strikes a horizontal surface. The ball leaves this surface 0.50 s later with a velocity
of 2.0 m/s directed 60 above the horizontal. What is the magnitude of the average resultant force
on the ball?
a. 14 N
b. 11 N
c. 18 N
d. 22 N
e. 3.0 N
____
Physics 115 Final Exam
____
8. A 10-g bullet moving 1000 m/s strikes and passes through a 2.0-kg block initially at rest, as
shown. The bullet emerges from the block with a speed of 400 m/s. To what maximum height
will the block rise above its initial position?
a.
b.
c.
d.
e.
____
8
78 cm
66 cm
56 cm
46 cm
37 cm
9. A wheel rotates about a fixed axis with an initial angular velocity of 20 rad/s. During a 5.0-s
interval the angular velocity decreases to 10 rad/s. Assume that the angular acceleration is
constant during the 5.0-s interval. How many radians does the wheel turn through during the 5.0-s
interval?
a. 95 rad
b. 85 rad
c. 65 rad
d. 75 rad
e. 125 rad
____ 10. A wheel (radius = 0.20 m) is mounted on a frictionless, horizontal axis. A light cord wrapped
around the wheel supports a 0.50-kg object, as shown in the figure. When released from rest the
object falls with a downward acceleration of 5.0 m/s2. What is the moment of inertia of the
wheel?
a.
b.
c.
d.
e.
0.023 kg  m2
0.027 kg  m2
0.016 kg  m2
0.019 kg  m2
0.032 kg  m2
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____ 11. Particles (mass of each = 0.40 kg) are placed at the 60-cm and 100-cm marks of a meter stick of
negligible mass. This rigid body is free to rotate about a frictionless pivot at the 0-cm end. The
body is released from rest in the horizontal position. What is the magnitude of the initial linear
acceleration of the end of the body opposite the pivot?
a. 15 m/s2
b. 9.8 m/s2
c. 5.8 m/s2
d. 12 m/s2
e. 4.7 m/s2
____ 12. A uniform ladder 15 ft long is leaning against a frictionless wall at an angle of 53 above the
horizontal. The weight of the ladder is 30 pounds. A 75-lb boy climbs 6.0-ft up the ladder. What
is the magnitude of the friction force exerted on the ladder by the floor?
a. 43 lb
b. 34 lb
c. 38 lb
d. 47 lb
e. 24 lb
____ 13. A uniform 100-lb beam is held in a vertical position by a pin at its lower end and a cable at its
upper end. A horizontal force (magnitude P) acts as shown in the figure. If P = 75 lb, what is the
tension in the cable?
a.
b.
c.
d.
e.
54 lb
69 lb
47 lb
61 lb
75 lb
____ 14. The motion of a particle connected to a spring is described by x = 10 sin (t). At what time (in s)
is the potential energy equal to the kinetic energy?
a. 0
b. 0.25
c. 0.50
d. 0.79
e. 1.0
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____ 15. The amplitude of a system moving with simple harmonic motion is doubled. The total energy will
then be
a. 4 times larger
b. 3 times larger
c. 2 times larger
d. the same as it was
e. half as much
____ 16. A 40-C charge is positioned on the x axis at x = 4.0 cm. Where should a 60-C charge be
placed to produce a net electric field of zero at the origin?
a. 5.3 cm
b. 5.7 cm
c. 4.9 cm
d. 6.0 cm
e. +6.0 cm
____ 17. A uniform linear charge density of 7.0 nC/m is distributed along the y axis from y = 2 m to y = 5
m. Which of the following integrals is correct for the magnitude (in N/C) of the electric field at y
= 0 on the y axis?
a.
b.
c.
d.
e. none of these
____ 18. A particle (m = 2.0 g, q = 5.0 nC) has a speed of 30 m/s at point A and moves (with only
electric forces acting on it) to point B where its speed is 80 m/s. Determine the electric potential
difference VA  VB.
a. 2.2 kV
b. +1.1 kV
c. 1.1 kV
d. +2.2 kV
e. +1.3 kV
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____ 19. A particle (charge = 40 C) moves directly toward a second particle (charge = 80 C) which is
held in a fixed position. At an instant when the distance between the two particles is 2.0 m, the
kinetic energy of the moving particle is 16 J. Determine the distance separating the two particles
when the moving particle is momentarily stopped.
a. 0.75 m
b. 0.84 m
c. 0.95 m
d. 0.68 m
e. 0.56 m
____ 20. A particle (q = 5.0 nC, m = 3.0 g) moves in a region where the magnetic field has components
Bx = 2.0 mT, By = 3.0 mT, and Bz = 4.0 mT. At an instant when the speed of the particle is 5.0
km/s and the direction of its velocity is 120 relative to the magnetic field, what is the magnitude
of the acceleration of the particle?
a. 33 m/s2
b. 17 m/s2
c. 39 m/s2
d. 25 m/s2
e. 45 m/s2
____ 21. A straight wire is bent into the shape shown. Determine the net magnetic force on the wire when
the current I travels in the direction shown in the magnetic field B.
a.
b.
c.
d.
e.
2IBL in the z direction
2IBL in the +z direction
4IBL in the +z direction
4IBL in the z direction
zero
____ 22. A proton is accelerated from rest through a potential difference of 150 V. It then enters a region
of uniform magnetic field and moves in a circular path (radius = 12 cm). What is the magnitude
of the magnetic field in this region?
a. 18 mT
b. 12 mT
c. 15 mT
d. 22 mT
e. 10 mT