phy 121
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A ball accelerates uniformly as it rolls 20 cm down a ramp, starting from rest, in 2 seconds.
• What are its average velocity, final velocity and acceleration?
answer/question/discussion: ->->->->->->->->->->->-> :
‘ds=20cm
‘dt=2 seconds
aAve=’ds/’dt=20cm/2 sec=10cm/sec
vAve=(vf-v0)/2=(10cm/sec-0)/2=5cm/sec
You mean
vAve=’ds/’dt=20cm/2 sec=10cm/sec
aAve=(vf-v0)/2=(10cm/sec-0)/2=5cm/sec
However vf is not 10 cm/s.
vf=’dv-v0=10cm/sec-0=10cm/sec
`dv = vf - v0.
`dv is not 10 cm/s.
#$&*
• If the time interval is in error so that it is 3% longer than the actual time interval, then what are the actual values of the final velocity and acceleration?
answer/question/discussion: ->->->->->->->->->->->-> :
vf= 9.7cm/sec
aAve=4.85cm/sec
This answer is incorrect. Be sure you compare with the link provided at the end of this document.
#$&*
• What is the percent error in each?
answer/question/discussion: ->->->->->->->->->->->-> :
( (10-9.7)/9.7) *100=3.1%
(5-4.85)/4.84) *100= 3.1%
#$&*
• If the percent error is the same for both velocity and acceleration, explain why this must be so.
answer/question/discussion: ->->->->->->->->->->->-> :
They were the same. This might be because the average velocity is only 5cm/s less than the average acceleration.
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• If the percent errors are different explain why it must be so.
answer/question/discussion: ->->->->->->->->->->->-> :
#$&*
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30 min
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Then please compare your solutions with the expanded discussion at the link
Solution
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