course Phy 121
13/Jul/2010 21:21
The problem: A ball starts with velocity 0 and accelerates uniformly down a ramp of length 30 cm, covering the distance in 5 seconds.
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What is its average velocity?
answer/question/discussion (start in the next line):
v_Ave = 30 cm / 5 sec = 6 cm /sec
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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):
Average Velocity = Initial Velocity + Final Velocity / 2
Final Velocity = Average Velocity * 2 - Initial Velocity
Final Velocity = 6 cm/sec * 2 -0 = 12 cm/sec
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By how much did its velocity therefore change?
answer/question/discussion (start in the next line):
Change in velocity = 12 cm/sec
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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):
Average Change in Velocity = 12 cm/sec / 5 sec = 2.4 (cm/sec) / sec
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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):
Positive Slope of 6, Linear, Rising left-to-right.
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