7. Position as a function of time of two moving objects is presented by the graph. Which of the following
statements is true?
I. Object II has a greater velocity than object I
II. Object II has a greater acceleration than object I
III. At time t
0
they have the same velocity
IV. At time t
0
object II passes by object I
A. I only B. I, II, and IV only C. I and IV only D. III and IV only E. II and IV only
Answer: (C). Lets look at each choice…
I. Object II has a greater velocity than object I (true! Slope of x vs. t equals velocity)
II. Object II has a greater acceleration than object I (no! both have a = 0)
III. At time t
0
they have the same velocity (no! slope = velocity)
IV. At time t
0
object II passes by object I ( true! At same position and II is faster)
8. In which of the following situations would an object be accelerated?
I. It moves in a straight line at constant speed.
II. It moves with uniform circular motion.
III. It travels as a projectile in a gravitational field with negligible air resistance.
(A) I only (B) III only (C) I and II only (D) II and III only (E) I, II, and III
Answer: (D) This involves 2d motion, so is not really appropriate for this test. However, the correct
answer is (D). Acceleration means changing velocity, which can change in magnitude or direction.