Question

A balanced lever has two weights on it, the first with mass `3 kg` and the second with mass `1 kg`. If the first weight is `7 m` from the fulcrum, how far is the second weight from the fulcrum?

Answer 1

`21m`

Explanation:

We apply the second condition for static equilibrium which states that the result torque (moments) must be zero,
ie. `sum vectau=0`, where `vectau=vecrxxvecF` is the cross product of the position vector from the axis of rotation (fulcrum) to the applied force and the applied force.

So in this case :

`r_1F_1-r_2F_2=0`

`therefore (7xx3g)-(r_2xx1g)=0`

`thereforer_2=(7xx3xx9.8)/(1xx9.8)=21m`.