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Aug 24, 2008

Sample Exam Problem 31




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2 comments:

nour said...

By intuition i agree that aA=aC.

But if we want to work this the way we used to earlier dont we get
xA+yC=L
aA=-aC
??

November 30, 2008 at 3:19 PM
CMK said...

In order for your equation xA + yC = L to be correct, yC would need to measure the position of C FROM the pulley (that is, yC would be positive DOWNWARD). However, I chose to measure y positively UPWARD. Therefore, the constraint would read something link xA - yC = constant. This gives xA_dot_dot = +yC_dot_dot.

Whichever approach that you use, it is best to test out the result when you are done. With the sign conventions used (xA positive to the right and yC positive up), an increase in xA corresponds to an increase in yC. From this, you know xA_dot_dot = +yC_dot_dot.

Let us know if this does not help.

November 30, 2008 at 4:04 PM

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