Question

An object with a mass of `7` `kg` is hanging from an axle with a radius of `36` `m`. If the wheel attached to the axle has a radius of `9` `m`, how much force must be applied to the wheel to keep the object from falling?

Answer 1

This is a similar case to a lever: the torque on both sides need to be the same for balance. `tau_1=rF=rmg=36*7*9.8=2469.6` `Nm`. `tau_2=rF to F=tau_2/r` but `tau_1=tau_2` so `F=2469.6/9=274.4` `N`.

Explanation:

I think the explanation above is clear, but it's worth pointing out that the force acting one the `7` `kg` mass is its weight force, `F=mg` where `g` is the acceleration due to gravity, `9.8` `ms^-2`.