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Phy 231
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.
** CQ_1_02.1_labelMessages.txt **
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):
7 cm/sec
Vave = ?
Vave = (Vf + vi) / 2 = ((10 + 4) cm / sec) / 2 = 7 cm / sec
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Without further information, why is this just a guess?
answer/question/discussion: ->->->->->->->->->->->-> (start in the next line):
This is just an average of two known velocities, I do not know how the velocity is changing, or not changing between the given intial and final velocities.
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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):
'dv = 'ds / d't
'dv * 'dt = 'ds
(10 cm/s - 4 cm/s) * 3 s = 18 cm
I think it travelled 18 cm from the first velocity to the second velocity.
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By your reasoning an object which traveled at a constant 30 cm/second for 5 seconds would travel (30 cm/s - 30 cm/s) * 5 s = 0 cm during this time.
The change in the velocity does not govern how far an object moves.
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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):
average rate = 'delta v / 'delta t = ((10 - 4) cm /s) / 3 s = (6 cm/s) / 3s = 2 cm/s^2
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This is correct. The change in velocity is required to calculate the average rate at which it changes.
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You made one very common error, and will need to revise that one calculation.
Otherwise very well done.
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