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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):
(9 sec, 28cm/s)
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• What is the velocity at the midpoint of this interval?
answer/question/discussion: ->->->->->->->->->->->-> (start in the next line):
28cm/s / 9s = 3.1cm/s/s
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You've divided the midpoint velocity by the midpoint clock time.
Dividing a velocity by the corresponding clock time does not give you an average velocity. (It doesn't given you an average acceleration either).
Sketch the graph, if you haven't already don so. Sketch the line segment connecting these two points. Then sketch the midpoint of this segment.
The coordinates of this point, as you have already said, are 9 sec and 28 cm/s.
The midpoint clock time is therefore 9 seconds.
What do you think the midpoint velocity is?
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Good.
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• How far do you think the object travels during this interval?
answer/question/discussion: ->->->->->->->->->->->-> (start in the next line):
If we take the average velocity, we can guess that the object traveled 28cm/s for 8 seconds, so roughly 224cm.
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• By how much does the clock time change during this interval?
answer/question/discussion: ->->->->->->->->->->->-> (start in the next line):
8 seconds
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• By how much does velocity change during this interval?
answer/question/discussion: ->->->->->->->->->->->-> (start in the next line):
24cm/s
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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):
(40cm/s - 16cm/s) / (13s - 5s) = 24cm/s / 8s = 3cm/s/s
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• What is the rise of the graph between these points?
answer/question/discussion: ->->->->->->->->->->->-> (start in the next line):
24
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• What is the run of the graph between these points?
answer/question/discussion: ->->->->->->->->->->->-> (start in the next line):
8
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• What is the slope of the graph between these points?
answer/question/discussion: ->->->->->->->->->->->-> (start in the next line):
3
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The rise, run and slope have units, so they should be specified with their appropriate units (in this case cm/s, s and cm/s^2, as you know).
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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):
This slope tells me that for every one second, the velocity increases by 3cm/s
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Very good, but see my notes. You overcomplicated one of the early questions.
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