Answer to Question #168384 in Physics for Andu

Question

At the ends of a light rod are hung bodies A and B with different masses. When the force meter depends on the point O (which is the axis of rotation), the rod stays in equilibrium. Calculate the weights of bodies A and B, when it is known that the force gauge shows the force 56 N. The distance from A to O is 20cm and the distance from B to O is 8 cm.

Answer 1

First, we need to understand two things: the rod weighs nothing and the weight that the force gauge shows is the total weight of A and B:

$$A+B=56\text{ N}.$$

Second, we need to understand that the torques created by A and B are equal:

$$A·20=B·8,\\\space\\ A=0.4B.$$

Substitute this into the very first equation:

$$0 .4B+B=56,\\ B=40\text{ N}.$$

According to the third equation,

$$A=0.4B=16\text{ N}.$$