Answer:
The box should be placed at a distance of [tex]\frac{r}{2}[/tex] from the pivot
Explanation:
In order to be in static equilibrium, both Torques have to be the same magnitude, so:
[tex]T_{m} = T_{2m}[/tex] Replacing the formula for Torque:
[tex]m*r = 2m*X[/tex] where X is the distance we need to find.
Solving for X we get:
[tex]X = \frac{r}{2}[/tex]
As we can see, the distance does not depend on the actual value of the mass but on the fact of one being twice as much as the other one.