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PHY 121
Your 'cq_1_02.2' 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_02.2_labelMessages **
The problem:
A graph is constructed representing velocity vs. clock time for the interval between clock times t = 5 seconds and t = 13 seconds. The graph consists of a straight line from the point (5 sec, 16 cm/s) to the point (13 sec, 40 cm/s).
What is the clock time at the midpoint of this interval?
answer/question/discussion: ->->->->->->->->->->->-> (start in the next line):
The clock time is 9 seconds. I drew the graph and found the midpoint. You can also find the mid point by adding 5 and 13 and dividing the sum by 2, which gets you 18/2 or 9.
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What is the velocity at the midpoint of this interval?
answer/question/discussion: ->->->->->->->->->->->-> (start in the next line):
The velocity is 3 cm/sec. I took the difference between this point and the starting point to determine this (28-16)/(9-5)=14/4 = 3 cm/sec.
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Your calculation does not lead to units of cm / sec.
(28-16)/(9-5) is therefore not a good calculation, though it's on the right track with the right numbers in the right places.
(28 cm/s -16 cm/s)/(9 s - 5 s) would be a good calculation, since the change in velocity 28 cm/s - 16 cm/s would take place in 4 seconds.
However the more appropriate calculation would be
(40 cm/s - 16 cm/s) / (13 s - 5 s)
since this applies to the entire interval. You're simply less likely to make an error if you use the whole interval, not to mention that this calculation involves only given numbers as opposed to numbers you calculated.
The answer would in any event be the same as for your calculation.
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How far do you think the object travels during this interval?
answer/question/discussion: ->->->->->->->->->->->-> (start in the next line):
It traveled from 16 to 28, which is a difference of 14 cm.
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The units of 16 and 28 aren't cm, and those numbers don't represent distances.
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By how much does the clock time change during this interval?
answer/question/discussion: ->->->->->->->->->->->-> (start in the next line):
The clock time changed from 5 to 9 during this interval, or 4 sec.
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That's for only half the given interval.
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By how much does velocity change during this interval?
answer/question/discussion: ->->->->->->->->->->->-> (start in the next line):
The velocity stays at 3 cm/sec during this interval.
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The velocity clearly changes during the interval.
The rate of change of the velocity with respect to clock time stays constant, but that rate does not have the units you give here.
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What is the average rate of change of velocity with respect to clock time on this interval?
answer/question/discussion: ->->->->->->->->->->->-> (start in the next line):
(28-16)/(9-5) = 12/4 = 3 cm/s
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What is the rise of the graph between these points?
answer/question/discussion: ->->->->->->->->->->->-> (start in the next line):
The rise is 3. It goes up 3 cm for each second.
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What is the run of the graph between these points?
answer/question/discussion: ->->->->->->->->->->->-> (start in the next line):
The run is 1. For each 3 cm gained it takes 1 second.
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What is the slope of the graph between these points?
answer/question/discussion: ->->->->->->->->->->->-> (start in the next line):
The slope is 3; rise/run is 3/1 or 3.
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What does the slope of the graph tell you about the motion of the object during this interval?
answer/question/discussion: ->->->->->->->->->->->-> (start in the next line):
The object is moving at a rate of 3 cm/sec during this interval.
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What is the average rate of change of the object's velocity with respect to clock time during this interval?
answer/question/discussion: ->->->->->->->->->->->-> (start in the next line):
The velocity remains 3 cm/s throughout the interval.
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*#&!
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You are definitely on the right track but your units aren't correct, and you are misinterpreting your results.
I believe you can nail this down with a revision.
&#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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