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PHY 121
Your 'cq_1_02.1' report has been received. Scroll down through the document to see any comments I might have inserted, and my final comment at the end.
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The problem:
A ball starts with velocity 4 cm/sec and ends with a velocity of 10 cm/sec.
What is your best guess about the ball's average velocity?
answer/question/discussion: ->->->->->->->->->->->-> n (start in the next line):
Assuming the ball traveled the 6cm in 1 sec
(10cm/sec-4cm/sec)/1sec
=6cm/sec/sec
=6cm/sec^2
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Without further information, why is this just a guess?
answer/question/discussion: ->->->->->->->->->->->-> n (start in the next line):
There is no information regarding the amount of time it took for the ball's velocity to change from 4cm/sec to 10cm/sec
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If it takes 3 seconds to get from the first velocity to the second, then what is your best guess about how far it traveled during that time?
answer/question/discussion: ->->->->->->->->->->->-> n (start in the next line):
vAve = `ds/`dt = (6cm/sec)/3s = 2cm/sec
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`ds is change in position.
6 cm/s is the change in velocity.
So `ds is not 6 cm/s.
So this calculation doesn't give you vAve
However your calculation would give you an important quantity. (note however that the units of this calculation, in which you divide cm/s by s, would not be cm/s)
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`ds = vAve * `dt
= 2cm/sec * 3sec
=6cm
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If vAve was 2 cm/s this would be correct.
However the average velocity is between 4 cm/s and 10 cm/s. It's not 2 cm/s.
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*#&!*#&!
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You got turned around on a couple of calculations. Spend a reasonable amount of time on a revision, but if you get bogged down be sure to ask questions.
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