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PHY 231
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): (40 + 16) / 2 = 28 cm/s at midpoint
Slope is (40 - 16) / (13 - 5) = 24 / 8 = 3 cm/s
28 cm/s - 16 cm/s = 12 cm/s
Since the movement is 3 cm/s, it took four seconds to reach the midpoint
So the midpoint was at 5 sec + 4 sec = 9 seconds
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What is the velocity at the midpoint of this interval?
answer/question/discussion: ->->->->->->->->->->->-> (start in the next line):
(9 sec, 28 cm/s)
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How far do you think the object travels during this interval?
answer/question/discussion: ->->->->->->->->->->->-> (start in the next line):
(5 sec, 16 cm/s) (6 sec, 19 cm/s) (7 sec, 22 cm/s) (8 sec, 25 cm/s) (9 sec, 28 cm/s)
16 + 19 + 22 + 25 + 28 = 110 cm
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The only interval mentioned is the 8-second interval from the first event to the last. Your calculation appears to address the subinterval from the initial event to the midpoint.
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This subinterval lasts only 4 seconds, yet your calculation shows displacements for each of five 1-second increments.
Your result would be valid for an object whose average velocities during each of five 1-second intervals were 16, 19, 22, 25 and 28 cm/s.
Would that be the same as, more than, or less than the displacement of this object during the 4-second subinterval you are considering?
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What would the the displacement of this object during the entire 8-second interval?
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By how much does the clock time change during this interval?
answer/question/discussion: ->->->->->->->->->->->-> (start in the next line): 9 sec - 5 sec = 4 seconds
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By how much does velocity change during this interval?
answer/question/discussion: ->->->->->->->->->->->-> (start in the next line):
28 cm/sec - 16 cm/sec = 12 cm/sec
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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):
In one second, 3cm/sec change
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What is the rise of the graph between these points?
answer/question/discussion: ->->->->->->->->->->->-> (start in the next line):
3 cm
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The graph is of velocity vs. clock time.
The rise of the graph would be in units of velocity. 3 cm is not a unit of velocity.
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What is the run of the graph between these points?
answer/question/discussion: ->->->->->->->->->->->-> (start in the next line):
1 sec
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'These points' can refer only to the points given in the statement of the problem. The run of the graph between those points is not 1 second.
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What is the slope of the graph between these points?
answer/question/discussion: ->->->->->->->->->->->-> (start in the next line):
3 cm/sec
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You need to base your result on the correct rise and run, and the units have to follow from the correct units of the rise and run.
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You do need to show your entire calculation.
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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 velocity in increasing
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The slope does tell you this, but it tells you much more.
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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):
In one second, 3cm/sec change
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You have a lot of the right ideas, but you haven't always applied them rigorously.
&#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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