Velocity from graphs of position versus time
Figure 2.9 shows graphs of an object’s position along the x axis versus time for four separate trials. Which of these statements is or are correct?
A. The velocity is greater in trial 2 than in trial 3.
B. The velocity is not constant during trial 1.
C. During trial 4, the object changes direction as it passes through the point x = 0.
D. The velocity is constant during trials 2, 3, and 4.
(Remember that velocity means “x component of velocity.”)
The graph of the motion during trial 1 has a changing slope and therefore \upsilon _x isn’t constant. Trials 2, 3, and 4 all have graphs with constant slope and thus correspond to motion with constant velocity. (The velocity is zero during trial 2, as indicated by the slope of zero, but this value is still constant.) Trial 3 has a positive velocity, while the velocity in trial 4 is negative. Thus, answers B and D are correct.