12 . Momentum of an isolated system always remains constant. However, in a collision between two
balls, a ball’s momentum might change from, say, +1 kg m/s to −1 kg m/s. How can this be correct?
(A) It is not correct. Momentum conservation means that the momentum of an object must remain the
same.
(B) A force outside the two-ball system must have acted.
(C) Friction is responsible for the change in momentum.
(D) Although one ball’s momentum changed, the momentum of both balls in total remained the same.
(E) Momentum is conserved because the magnitude of the ball’s momentum remained the same.
Circular motion
13 . Which of the following must be true of an object in uniform circular motion?
(A) Its velocity must be constant.
(B) Its acceleration and its velocity must be in opposite directions.
(C) Its acceleration and its velocity must be perpendicular to each other.
(D) It must experience a force away from the center of the circle.
(E) Its acceleration must be negative.Harmonic motion
14 . A mass on a spring has a frequency of 2.5 Hz and an amplitude of 0.05 m. What is the period of the
oscillations?
(A) 0.4 s
(B) 0.2 s
(C) 8 s
(D) 20 s
(E) 50 s
15 . A mass m oscillates on a horizontal spring of constant k with no damping. The amplitude of the
oscillation is A . What is the potential energy of the mass at its maximum displacement?
(A) zero
(B) mgh
(C) kA
(D) ½mv 2
(E) ½kA 2
Rotational motion
16 . A ball of mass m is spinning about a diameter. If it were instead to make twice as many rotations per
second, what would happen to the ball’s rotational inertia and its angular momentum?