phy 121
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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):
average velocity=’ds/’dt
30cm/5sec=6cm/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):
avg=I-F
6=0-F
Final Velocity=6cm/sec
if the final velocity is 6 cm/s then the average velocity is the average (6 cm/s + 0 cm/2) / 2 = 3 cm/s of the initial and final velocities.
However we already know that the average velocity is 6 cm/s. So the final velocity can't be 6 cm/s.
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• By how much did its velocity therefore change?
answer/question/discussion: ->->->->->->->->->->->-> (start in the next line):
It’s average and final velocity are the same. I do not think that this can be correct but if it’s average is 6cm/sec and you plug that into the formula then you get the same thing for the final as you do for the average.
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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 rate=’dV/’dt
6cm/sec/5sec=1.2cm/s/s
if the final velocity was 6 cm/s this would be 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):
The Y axis would be the velocity and the X axis would be the time. For this particular problem it would be increasing at a slow rate.
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20 minutes
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&#See any notes I might have inserted into your document. If there are no notes, this does not mean that your solution is completely correct.
Then please compare your solutions with the expanded discussion at the link
Solution
Self-critique your solutions, if this is necessary, according to the usual criteria. Insert any revisions, questions, etc. into a copy of this posted document. Mark any insertions with &&&& so they can be easily identified.If your solution is completely consistent with the given solution, you need do nothing further with this problem. &#