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

My friend wanted me to explain this problem, it seems pretty simple but I can't get the back of the book answer.

a wheel 60 cm in radius is connected to an axle that is 1.5 cm in radius. Someone pulls with a force of 50 N on a thin cord wrapped around the axle. How much force do you have to exert on the wheel's rim to hold it still?

3. The attempt at a solution

First I tried a simple torque balancing but that doesnt work: 60cm * x N = 1.5 cm * 50 N -> x = 1.25 N.

Then I thought, maybe the wheel has friction with the ground, because torque AND force must be balanced in static equilibrium, so:

x (the force) * 60 cm - (50N - x) (frictional force that prevents slipping) * 60 cm = 50 N * 1.5 cm. But that makes an answer near 25ish N, obviously because these torques are large compared to the one around the axle.

So the correct answer is supposed to be 6.1 N but I can't get it, can anyone explain it to me? I really like this friend and I would appreciate it :)

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# Homework Help: Rotational problem

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