Question

A force $F$ is applied on free end of a string such mass of $18kg$ remain stationary. Then value of $F$ will be:

• A. $180N$
• B. $90N$
• C. $60N$
• D. $30N$

Answer 1

The correct option is B $90N$

Observe the forces acting on pulley are applying $2T$ in upward direction and $mg$ in downward, so for block to be at rest, accelaration of pulley must be zero.

Hence:

$2T-18g=18a$

$T=90N$