PHY 121
Your 'cq_1_9.1' 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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Seed Question Assignment 9
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:
‘dt = 2 sec
‘ds = 20 cm
vAve = 20 cm/2 sec = 10 cm/sec
vf = 2 * vAve = 2 * 10 cm/s = 20 cm/s
a = ‘dv / ‘dt = (20 cm/s – 0 cm/s) / 2 s = 10 cm/s^2
• 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:
103/100 = 2s/’dt
200 s / 103 = ‘dt
‘dt = 1.94 s
vAve = 20 cm/1.94 s = 10.31 cm/s
vf = 2*10.31 cm/s = 20.62 cm/s
a = 20.62 cm/s / 2 s = 10.31 cm/s^2
With the 3% error, `dt is 1.94 seconds, which you used in calculating the average velocity.
However you used 2 s in calculating the acceleration.
• What is the percent error in each?
answer/question/discussion:
% error vf = (20 cm/s – 20.62 cm/s) / 20.62 cm/s = (- .62 cm/s) / 20.62 cm/s = 3 %
% error a = (10 cm/s^2 – 10.31 cm/s^2) / 10.31 cm/s^2 = 3%
• If the percent error is the same for both velocity and acceleration, explain why this must be so.
answer/question/discussion:
The percent error is the same as the percentage of difference in the numbers used to calculate the answers because the percent error is actually just the deviation from the correct answer. The ‘dt numbers differ by 3%, therefore the answers to problems where ‘dt is used will differ by 3%.
• If the percent errors are different explain why it must be so.
answer/question/discussion:
n/a
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20 MIN
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See my note and be sure you understand your error. No revision is necessary as long as you understand the notes at the links below.
&#At least part of your solution does not agree with the solution and comments given at the link below. You should view the solution at that link and self-critique as indicated there.
Solution
This link also expands on these topics and alerts you to many of the common errors made by students in the first part of this course. &#