Question

Two wires are made of the same material and have the same volume. The first wire has cross-sectional area A and the second wire has cross-sectional area 3A. If the length of the first wire is increased by ∆l on applying a force F, how much force is needed to stretch the second wire by the same amount?

(A) 9 F 

(B) 6 F 

(C) 4 F 

(D) F

Answer 1

(A) 9 F

As material is same, Young’s modulus of two wires is same.

Also, volume of both wires is same.

V₁ = V₂

To stretch the second wire through same length (△l), let force needed be F'