Question

In Figure, a block of weight $15N$ is hanging from a rigid support by a string. What force is exerted by
(a) block on the string,
(b) string on the block.

• A. (a) $15$ $N$ downwards , (b) $15$ $N$ upwards
• B. (a) $15$ $N$ downwards , (b) $15$ $N$ downwards
• C. (a) $15$ $N$ upwards , (b) $15$ $N$ upwards
• D. (a) $15$ $N$ upwards , (b) $15$ $N$ downwards

Answer 1

The correct option is A (a) $15$ $N$ downwards , (b) $15$ $N$ upwards

(a) Block has a tendency to fall towards the ground. Therefore, block exerts a downward force on the string which is equal to its weight i.e. $15N$.
(b) Since, system is balanced and motionless, all the forces will be balanced. Due to weight of the block, an equal and opposite tension force is acting on the string. Therefore, string exerts a force of $15N$ in the upward direction.