EXAM PRACTICE 3 PHYS 15200
NOTE
1) Your official exam will have different questions.
2) You will be tested on your mastery of concepts and problem-solving skills.
3) You will be given a formula sheet to use during the exam.
3) The solutions to this practice exam will be discussed in lecture.
Part I. Multiple Choice Questions [2 pts each]
Directions: Choose the alternative that best completes the statement or answers the question. Unless
otherwise stated, assume ideal conditions (no air resistance, uniform gravity, etc.)
1) A constant nonzero net torque is exerted on an object. Which of the following statements is true
regarding the motion of the object? (Only one choice is possible.)
(A) It has zero angular velocity.
(C) It has a constant nonzero angular acceleration.
(B) It has zero angular acceleration.
(D) None of these.
2) A balls rolls without slipping down the incline plane shown in the
diagram. What is the direction of its angular acceleration vector?
(A) into the page
(C) up the incline
(E) None of these.
(B) out of the page
(D) down the incline
3) An iceskater is spinning about a vertical axis through her center of mass. She initially holds her arms
close to her body. She then stretches out her arms away from her body such that her moment of inertia
increases by a factor of two. How does her kinetic energy change?
(A) decreases by a factor of 2
(C) decreases by a factor of 4
(E) None of these
(B) increases by a factor of 2
(D) increases by a factor of 4
4) A spherical shell of mass M and radius R has a moment of inertia Icm about its
center of mass. Which expression correctly describes the moment of inertia of the
rod+ball system about the axis shown in the diagram?
(A) Icm + MR2
(C) Icm + 3MR2
(E) None of the above
(B) Icm + 2MR2
(D) Icm + 4MR2
2R
axis
5) Consider a coin sitting on a horizontal spinning disk, a radius r from its axis of rotation. The disk is
spinning about its center of mass at constant speed. Which of the following quantities is nonzero for the
coin? (Only one choice is possible.)
(A) net torque
(C) tangential velocity
(E) None the of above
(B) angular acceleration
(D) tangential acceleration
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PRACTICE EXAM 3 PHYS 15200
Part II. Word Problems [30 pts each]
Directions: Solve each problem. Show your work to receive full credit. Box your final answer and record
its appropriate unit.
1)
0.300 N
A spool consists of a cylinder of radius 2.00 cm bonded to a cylinder of radius 4.00 cm. The spool has a
mass 0.280 kg and a moment of inertia 3.36104 kg-m2 about its center. Massless thread is wrapped
around the smaller cylinder. The spool sits initially at rest on a flat table with friction. A constant
horizontal force of 0.300 N pulls the thread to the right. As a result, the spool rolls to the right without
slipping.
(A) What is the linear acceleration of the center of the spool?
(B) What is its angular speed in 2.00 s?
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PRACTICE EXAM 3 PHYS 15200
2)
A uniform solid ball (mass M, radius R) attached to one end of a massless string to form a pendulum.
The other end of the string is attached to a pivot at the ceiling. The pendulum is initially held at rest
horizontally and then released. When the pendulum reaches the vertical position, it strikes a block (mass
M) initially at rest along a frictionless flat surface. Assume that the collision is inelastic.
(A) What is the angular speed of the pendulum when it reaches the vertical position?
(B) Suppose that the angular speed of the pendulum immediately after the collision is exactly half the
value you found in Part A. What is the linear speed of the block immediately after the collision?
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PRACTICE EXAM 3 PHYS 15200
3)
cable
50
L
A uniform beam (mass 40.0 kg, length L) is hinged to the floor at one end. The beam is held at 50 to
the floor by a cable attached to the other end. A load of mass 20.0 kg hangs at rest from the same end.
(A) What is the tension in the cable?
(B) What is the horizontal contact force on the beam exerted by the hinge?
(C) What is the vertical contact force on the beam exerted by the hinge?
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