#$&*
course Phys201
6/10 @7:42pm
If the velocity of the object changes from 3 cm / sec to 13 cm / sec in 7 seconds, then at what average rate is the velocity changing?vAve=`ds/`dt
vAve=13-3/7
vAve=10/7
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`` You need to use units throughout your calculation, and actually do the algebra of the units.
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vAve=1.43 cm/sec
A ball rolling from rest down a constant incline requires 9.6 seconds to roll the 99 centimeter length of the incline.
• What is its average velocity?
vAve=`ds/`dt
=99cm/9.6sec
=10.3 cm/sec
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This calculation is done correctly.
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An object which accelerates uniformly from rest will attain a final velocity which is double its average velocity.
• What therefore is the final velocity of this ball?
• What average rate is the velocity of the ball therefore changing?
vf=0
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The ball has average velocity 10.3 cm/s.
An object which accelerates uniformly from rest will attain a final velocity which is double its average velocity.
It does not follow that vf = 0.
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The average rate is not changing. We know this because the problem states that the object accelerates uniformly.
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The average rate of change of the ball's velocity is not zero.
That means that the velocity of the ball is changing. If it wasn't, then this average rate of change would be zero.
Uniform acceleration means that the rate of change of the velocity is not changing, so the rate is always equal to the average rate.
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An automobile accelerates uniformly down a constant incline, starting from rest. It requires 16 seconds to cover a distance of 120 meters. At what average rate is the velocity of the automobile therefore changing?
vAve=`ds/`dt
dt=16 sec
ds=120m
vAve=120/16
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`` You need to use units throughout your calculation, and actually do the algebra of the units.
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vAve=7.5m/s
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You have found the autmobile's average velocity.
You have yet not found the average rate of change of its velocity with respect to clock time, which is what was requested.
The preceding series of questions shows you how to reason this out.
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You are doing some good thinking, but as is commonly the case at this point you are making some errors.
I believe you'll be able to make corrections without too much trouble, based on the notes I've inserted.
&#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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