# Top spun up with string under tension problem [duplicate]

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I have a top with an unknown mass. It has a moment of inertia of 4.00 * 10^-7 kgm^2 a string is wrapped around the top and pulls it so that its tension is kept at 5.57 N for a distance of .8 m.

Could somebody help me derive some equations to help with this? Or to get me in the right direction? I have been trying to derive some sort of equations from KEr = 1/2 * I * w^2 but I cant get anywhere without ending up at radius = radius or mass = mass.

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## migrated from math.stackexchange.comMar 5 '11 at 0:17

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## marked as duplicate by mbqMar 6 '11 at 20:08

Hint: The work done on the top is force times distance. So given the MOI you can find $\omega$.