1. Marissa’s car accelerates uniformly at a rate of +2.60 m/s2. How long does it take for Marissa’s car to accelerate from a speed of 24.6 m/s to a speed of 26.8 m/s? 2. A bowling ball with a negative initial velocity slows down as it rolls down the lane toward the pins. Is the bowling ball’s acceleration positive or negative as it rolls toward the pins? 3. Nathan accelerates his skateboard uniformly along a straight path from rest to 12.5 m/s in 2.5 s. a. What is Nathan’s acceleration? b. What is Nathan’s displacement during this time interval? c. What is Nathan’s average velocity during this time interval? 4. Critical Thinking Two cars are moving in the same direction in parallel lanes along a highway. At some instant, the instantaneous velocity of car A exceeds the instantaneous velocity of car B. Does this mean that car A’s acceleration is greater than car B’s? Explain, and use examples. 5. Interpreting Graphics The velocity-versus-time graph for a shuttle bus moving along a straight path is shown in Figure 13. a. Identify the time intervals during which the velocity of the shuttle bus 8.0 is constant. 7.0 b. Identify the time intervals during 6.0 5.0 which the acceleration of the shuttle 4.0 3.0 bus is constant. 2.0 1.0 c. Find the value for the average veloc0 −1.0 100 200 300 400 500 600 ity of the shuttle bus during each −2.0 time interval identified in b. −3.0 −4.0 d. Find the acceleration of the shuttle −5.0 −6.0 bus during each time interval identi−7.0 −8.0 fied in b. Time (s) e. Identify the times at which the velocity of the shuttle bus is zero. Figure 13 f. Identify the times at which the acceleration of the shuttle bus is zero. g. Explain what the slope of the graph reveals about the acceleration in each time interval. 6. Interpreting Graphics Is the shuttle bus in item 5 always moving in the same direction? Explain, and refer to the time intervals shown on the graph. Velocity (m/s)
Section review answers
1. 0.85 s 2. positive 3. a. +5.0 m/s2 b. +16 m c. +6.4 m/s 4. No, car A’s acceleration is not necessarily greater than car B’s acceleration; If the two cars are moving in the positive direction, car A could be slowing down (negative acceleration) while car B is speeding up (positive acceleration),
even though car A’s velocity is greater than car B’s velocity. 5. a. 0 s to 30 s; 60 s to 125 s; 210 s to 275 s b. 0 s to 30 s; 30 s to 60 s; 60 s to 125 s; 125 s to 210 s; 210 s to 275 s; 275 s to 300 s; 300 s to 520 s; 520 s to 580 s c. 0 m/s; 1.5 m/s; 0 m/s; 1.5 m/s; 0 m/s; −0.75 m/s; −3.25 m/s; −4.5 m/s d. 0 m/s2; 0.1 m/s2; 0 m/s2; −0.04 m/s2; 0 m/s2; −0.06 m/s2; −0.02 m/s2; 0.02 m/s2 e. 0 to 30 s; 210 to 275 s f. 0 s to 30s; 60 s to 125 s; 210 s to 275 s g. When the graph slopes upward, acceleration is positive. When it slopes downward, acceleration is negative. 6. No; The bus is moving in the positive direction from 30 s to 210 s (when velocity is positive) and in the negative direction from 275 s to 600 s (when velocity is negative).
Motion in One Dimension