The axle of a pulley of mass `1 kg` is attached to the end of an elastic string of length `1m`, cross- sectional area `10^(-3) m^(2)` and young's modulus `2xx10^(5) Nm^(-2) `,whose other end is fixed to the ceiling. A rope of negligible mass is placed on the pulley such that its left end is fixed to the ground and its right end is hanging freely , from the pulley which is at rest in equilibrium . Now, the rope and the pulley can be neglected. (Given, `g = 10 ms^(-2)`)

The elongation of the string before applying force is

Options

A. `50 cm`
B. `60 cm`
C. `40 cm`
D. `50 cm`

Answer

D

Explanation

When the displacement of the pulley is `25 cm` , the string gets loosened on both the sides . So , Point `A` moves down by `50 cm `.