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Solution for Longanswer Homework 3 Motion problems
Solution to Longanswer Homework Problem 3.1(Motion diagrams)
Problem:
Let’s think back to some of the data analysis we have done in lab.
(a)Given the theoretical line below, sketch in how you would expect the data to look for 10 data points
for systematic and random error. You don’t have to get too technical, but in a few words in the
space below them, explain the diFerence in your drawings.
random
systematic
(b)Why do we like to plot things in a straight line relationship and get our answer from the slope when
we can?
(c)Let’s say we knew what the theoretical
y

intercept should be for our straight line. If we had a
systematic error, would we want to include this as a data point? Why or why not?
Solution to Part (a)
A systematic error always aFects the data the same way, like having a slightly chipped ruler, or having friction
in the system. A random error can ±uctuate, so sometimes you err a little high, and sometimes a little low, like
running a timer, or using any other measuring device.
Grading Key: Part (a) 11 Points
2 point(s) : A few words meaning: Systematic always same way
2 point(s) : A few words meaning: random ±uctuates
1 point(s) : data points all either above or below on systematic
2 point(s) : the slope of the line you would draw through the data points on
systematic is same as theoretical line
1 point(s) : data points scattered above and below on random
2 point(s) : the slope of the line you would draw through the data points on
random is same as theoretical line
1 point(s) : used approximately 10 points as asked on each graph
Solution to Part (b)
It is a graphical way to use the brain to calculate the weighted error. Or, something about how the use of a
straight line helps correct for random error. A point back towards points missed elsewhere if they discuss how the
slope of a line is unaFected by systematic error.
1
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View Full DocumentGrading Key: Part (b) 3 Points
3 point(s) : 3 if reasonable, 2 pts if sort of, 1 pt if anything salvageable
Solution to Part (c)
For a systematic error you do NOT want to force the yintercept, since all your data is o± in the same direction.
Grading Key: Part (c) 4 Points
2 point(s) : No (unless they got random and systematic confused in a)
2 point(s) : Theoretical yintercept does not have error, and since error all
in same direction, would skew the slope. (Does not have to be exact, but
clear they understand this. 1 pt if not really clear, but you can tell they sort
of understood.)
Total Points for Problem: 18 Points
Solution to Longanswer Homework Problem 3.2()
Problem:
Starting at the origin, particle
A
moves in the positive
ˆ
x
direction at
1
m
s
for
5
seconds, while particle
B
moves in the positive
ˆ
y
direction at
1
m
s
for
5
seconds. Both particles stop at
t
= 5s
.
(a)What was the speed of each particle?
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 Spring '08
 Stewart
 Physics, Work

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