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A mass m1 moves without any friction in a circle with radius r on a table. On to this mass a string is attached that goes through a hole in the table and is attached to another mass m2 under the table.

http://img358.imageshack.us/img358/5636/circularmotion0ny.gif [Broken]

There is no friction between the rope and the table. Derive a formula for the radius r in terms of m1, m2 and the time T for one complete revolution.

What I did is the following:

F= mtot * a, with a= ac= v^2/r

Therefore F= mtot * (v^2/r)

v= 2pi r/T. Substitution gives:

F= mtot * ((2pi r/T)^2)/ r = (mtot 4pi^2 r^2)/ (r T^2) = (mtot 4pi^2 r)/ T^2

so this gives r= (FT^2)/ (mtot 4 pi^2)...

But how will I get rid of the F term in the formula? Or is there some other way to solve this problem?

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# Homework Help: Tricky circular motion question

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