(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

A solid uniform disk of mass 21.0 and radius 85.0 is at rest flat on a frictionless surface. The figure shows a view from above. A string is wrapped around the rim of the disk and a constant force of 35.0 is applied to the string. The string does not slip on the rim.

(i) When the disk has moved a distance of 5.0 m, determine how fast it is moving.

(ii) How fast it is spinning (in radians per second)

(iii) How much string has unwrapped from around the rim.

2. Relevant equations

Work = tau * theta

rotational energy = 0.5I (omega)^2

translational KE = 0.5Mv^2

3. The attempt at a solution

I have tried using energy conservation but for some reason the answer isn't right. tau = 35*0.85. But I'm having trouble finding theta. I used theta = 5 / 0.85 but that isnt working since that would mean that the answer to question (iii) is 5 which it isn't. The work done equals the translational and kinetic energy. But without a correct theta, I can't work out any of the problem. The problem is from Physics for Scientists and Engineers by Giancoli Chapter 10, Problem 108

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# Homework Help: Disc pulled by a string

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