Stumped - work done by rotating mass

  • #1
1,197
1
stumped -- work done by rotating mass

the question is http://home.earthlink.net/~urban-xrisis/clip_image002.jpg [Broken]

I got the answers to questions (A) and (B) but I cant get (C)
My work is shown http://home.earthlink.net/~urban-xrisis/clip001.jpg [Broken]

the books gives me an answer of [tex]W=0.5mv_i^2(r_i^2/r^2-1)[/tex]


any help on where I went wrong?
 
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Answers and Replies

  • #2
Doc Al
Mentor
44,994
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You went wrong when you tried to find the work by multiplying the tension by [itex]r_i - r[/itex], which treats the tension as though it were constant. (It's not.) Instead, you must integrate to find the work done, since the tension is a function of r.
 

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