Question

How to find the weight of a given body using parallelogram law of vectors observations?

Answer 1

The parallelogram law of forces setup is used to determine the weight of the given load.

Taking the unknown weight of the load as S and weight suspended on either side of the hanger are P and Q.

Now slotting different weights in the hangers, the unknown weight would move up or down. The positions of the strings are marked on a paper in such a way that the three strings of each load is at the normal point.

Now using the formula,

$S=\sqrt{P^2+Q^2+2PQ\ cos\ cos\theta}$  

Here $\theta$ is the angle made between the strings of the slotted load.