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Chapter 2: Q14CQ (page 79)
Is it possible for velocity to be constant while acceleration is not zero? Explain.
No, it is not possible for velocity to be constant while acceleration is not zero.
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What information do you need in order to choose which equation or equations to use to solve a problem? Explain.
A football quarterback runs 15.0 m straight down the playing field in 2.50 s. He is then hit and pushed 3.00 m straight backward in 1.75 s. He breaks the tackle and runs straight forward another 21.0 m in 5.20 s. Calculate his average velocity (a) for each of the three intervals and (b) for the entire motion.
Freight trains can produce only relatively small accelerations and decelerations.
(a) What is the final velocity of a freight train that accelerates at a rate of\({\bf{0}}.{\bf{0500}}{\rm{ }}{\bf{m}}/{{\bf{s}}^{\bf{2}}}\)for\({\bf{8}}.{\bf{00}}{\rm{ }}{\bf{min}}\), starting with an initial velocity of\({\bf{4}}.{\bf{00}}{\rm{ }}{\bf{m}}/{\bf{s}}\)?
(b) If the train can slow down at a rate of\({\bf{0}}.{\bf{0500}}{\rm{ }}{\bf{m}}/{{\bf{s}}^{\bf{2}}}\), how long will it take to come to a stop from this velocity?
(c) How far will it travel in each case?
If you divide the total distance travelled on a car trip (as determined by the odometer) by the time for the trip, are you calculating the average speed or the magnitude of the average velocity? Under what circumstances are these two quantities the same?
Consider the velocity vs. time graph of a person in an elevator shown in Figure 2.58. Suppose the elevator is initially at rest. It then accelerates for, maintains that velocity for, then decelerates foruntil it stops. The acceleration for the entire trip is not constant so we cannot use the equations of motion from Motion Equations for Constant Acceleration in One Dimension for the complete trip. (We could, however, use them in the three individual sections where acceleration is a constant.) Sketch graphs of
(a) position vs. time and
(b) acceleration vs. time for this trip.
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