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Atwood's machine problem



Hello all,

I just got a question I can't answer, and could use some help.

A student got this problem out of a book (didn't tell which one) and asked
me, and I 'clutched':

An Atwood's machine is in perfect balance, with equal weights on both
sides. One of the weights is a monkey, and the other is a stack of
bananas. The monkey begins to climb at a constant speed. What happens to
the bananas; ie, do they rise, fall, or stay stationary.

My first inclination was to use CM and say that if the monkey climbs the
bananas must fall to keep the CM stationary. However, the book he Xeroxed
this from, said the bananas rise with the monkey.

Maybe it's just because it's Friday, but I don't see the 'mechanism' for
that explanation. Can somebody help?

Thanks,
Peter Schoch
(sleep deprived with a 15 month at home)