On suspending a weight M g, the length l of elastic wire having area of cross-section A, becomes double the initial length. The instantaneous stress action on the wire is

Question

On suspending a weight M g, the length l of elastic wire having area of cross-section A, becomes double the initial length. The instantaneous stress action on the wire is (A) M g / A (B) M g / 2 A (C) 2 M g / A (D) 4 M g / A

Tardigrade Admin · Accepted Answer

When the length of wire becomes doubled, its area of cross-section will become half because volume of wire is constant

(V = A L)

.
So, the instantaneous stress

= \frac{force}{area} = \frac{M g}{A /2} = \frac{2 M g}{A}

Q. On suspending a weight $M g$ , the length $l$ of elastic wire having area of cross-section $A$ , becomes double the initial length. The instantaneous stress action on the wire is

$M g / A$

$M g /2 A$

$2 M g / A$

$4 M g / A$

When the length of wire becomes doubled, its area of cross-section will become half because volume of wire is constant $(V = A L)$ .
So, the instantaneous stress $= \frac{force}{area} = \frac{M g}{A /2} = \frac{2 M g}{A}$

Q. On suspending a weight Mg, the length l of elastic wire having area of cross-section A, becomes double the initial length. The instantaneous stress action on the wire is

Mg/A

Mg/2A

2Mg/A

4Mg/A