Question

A wire with a radius of 5mm is hung freely from the ceiling. A load of 5N is applied to its free end. Find the elongation in the wire if its volume is 7.85*10^-5m^3 & young’s modulus is 10^11N/m^2.

(a) 6.21*10^-7m

(b) 7.00*10^-7m

(c) 6.36*10^-7m

(d) 8.00*10^-9m

This question was addressed to me in a job interview.

I'm obligated to ask this question of Solids Mechanical Properties topic in chapter Mechanical Properties of Solids of Physics – Class 11

Answer 1

Right option is (c) 6.36*10^-7m

Explanation: The initial length of wire is Vol / πr^2  = 7.85*10^-5/ π*0.005^2 = 1m.

Stress = Y*strain. F/A = Y*Δl / l.

Δl = F/A * l/Y                                                                                                                                                                                     = (5/πr^2)*(1/10^11)

= 6.37*10^-7m.