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course Phy 121
9/9 4:40
The problem:A ball starts with velocity 0 and accelerates uniformly down a ramp of length 30 cm, covering the distance in 5 seconds.
What is its average velocity?
answer/question/discussion (start in the next line):
ave vel = change in time / change in length
30 cm / 5 sec = 6 cm/s
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If the acceleration of the ball is uniform then its average velocity is equal to the average of its initial and final velocities.
You know its average velocity, and you know the initial velocity is zero.
What therefore must be the final velocity?
answer/question/discussion (start in the next line):
final velocity = ave vel * 2
final vel = 6 cm/s * 2
final vel = 12 cm/s
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By how much did its velocity therefore change?
answer/question/discussion (start in the next line):
the velocity change 12 cm/s - 0 cm/s = 12 cm/s
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At what average rate did its velocity change with respect to clock time?
answer/question/discussion (start in the next line):
the ave rate of change = change of A / change of B
Ave rate = change in distance / change in time
ave rate = 12 cm/s / 5 s
ave rate = 2.4 cm
Good, except that the units of your final result are not correct.
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What would a graph of its velocity vs. clock time look like? Give the best description you can.
answer/question/discussion (start in the next line):
It would have a positive slope of 2.4 each time. it would be a straight line.
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