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course Phy 121
10:15 pm June 10
cq_1_031#$&*
Your 'cq_1_03.1' report has been received. Scroll down through the document to see any comments I might have inserted, and my final comment at the end.
** CQ_1_03.1_labelMessages.txt **
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):
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30/5= 6
6 cm/sec= average velocity
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?
= (the initial velocity + average velocity)/2
= (0 + 6)/2
= 3 cm/s
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At this point you are saying that the initial velocity is 0 cm/s, the average velocity is 6 cm/s and the final velocity is 3 cm / s.
If the initial and final velocities are 0 cm/s and 3 cm/s, what is the average velocity? Note that the average velocity is between the initial and final velocities.
How does this result lead to a contradiction with the given information?
*@ &&&& If the initial velocity is 0 cm/s and the final is 3 cm/s then you would add the two and divide by 2. 3/2= 1.5 cm/sec.. This is a contradiction because I have average velocity at cm/sec which doesn’t make sense after working it out this way.
Is going on average 6 cm/sec and it covers 30 cm in 5 seconds. So if it is going 6 cm per second it would be 30 cm/s for the final.
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If it started at 0 cm/s and ended up at 30 cm/s, what would be the average?
Note that the average is 6 cm/s. Is this consistent with initial and final velocities 0 cm/s and 30 cm/s?
*@&&&yes
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If the initial velocity is 0 cm/s and the final is 30 cm/s, then assuming uniform acceleration the average velocity would have to be 15 cm/s, halfway between the initial and final.
Initial velocity 0 cm/s, average velocity 6 cm/s and final velocity 30 cm/s is not compatible with the condition of uniform acceleration.
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answer/question/discussion: ->->->->->->->->->->->-> (start in the next line):
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By how much did its velocity therefore change?
answer/question/discussion: ->->->->->->->->->->->-> (start in the next line):
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Change in initial and final velocities: 0 and 30= 30 cm/s
At what average rate did its velocity change with respect to clock time?
answer/question/discussion: ->->->->->->->->->->->-> (start in the next line):
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It went from 0 to 30 in 5 seconds.
Changed on average 30/5= 6 cm/s
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 increase at an increasing rate
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** **
20 minutes
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There are some inconsistencies in your results, which I've pointed out in inserted notes.
Spend up to 20 minutes trying to work out those contradicions, apply the definitions, etc., the submit your best revision according to my instructions below.
&#Please see my notes and submit a copy of this document with revisions, comments and/or questions, and mark your insertions with &&&& (please mark each insertion at the beginning and at the end).
Be sure to include the entire document, including my notes.
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Self-critique (if necessary):
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Self-critique rating:
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See my notes before answering these questions.
If initial velocityi is 0 cm/s, as given, and average velocity is 6 cm/s, as you figured out early in the problem, then what is the final velocity?
Now that you know initial velocity, final velocity and time interval, how do you find the average rate at which velocity changes with respect to clock time?
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&#Please see my notes and submit a copy of this document with revisions, comments and/or questions, and mark your insertions with &&&& (please mark each insertion at the beginning and at the end).
Be sure to include the entire document, including my notes. &#
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