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Phy 201
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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Asst 2 Question 1
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: ->->->->->->->->->->->-> (start in the next line):
Maybe 6 cm/sec?????
@& If an automobile speeds up from 60 mph to 65 mph, in some undetermined time interval, its velocity changes by 5 mph but it is not moving at an average of 5 mph. You would expect the average to be between 60 mph and 65 mph; and if it speeds up at a uniform rate you would expect the average to be 62.5 mph. You don't know what really happened, but your best guess would put the average velocity between the initial and final velocities.
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I’m confused about how to do this without knowing how many seconds the trial lasted. Would you just do the final velocity minus the initial????
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• Without further information, why is this just a guess?
answer/question/discussion: ->->->->->->->->->->->-> (start in the next line):
Because we don’t know the length of time.
@& More importantly we don't know how the velocity fluctuated between the two times.*@
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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: ->->->->->->->->->->->-> (start in the next line):
If the average is 6 cm/sec, it would travel 18 cm in 3 seconds. This is found by multiplying the average velocity by the amount of time during which the object is traveling.
@& That would be the correct way to get the result. 6 cm/s is not an implausible average velocity, being between 4 cm/s and 10 cm/s, and the displacement that would follow this estimate would be 18 cm. However you would not find average velocity by subtracting velocities; as in the example I gave previously that will usually lead to an unrealistic result.*@
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• At what average rate did its velocity change with respect to clock time during this interval?
answer/question/discussion: ->->->->->->->->->->->-> (start in the next line):
10 - 4 / 3 - 0 = 6 / 3 = 2
@& That would be correct, but you need to include units, and really should relate the calculation to the definition of an average rate of change.*@
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About 10 minutes
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