A wire has a young’s modulus of 10^5N/m^2, length 1m & radius 3mm. Assuming a uniform cross sectional area, find the radius of wire after it is under a force of 1N from both ends. (a) 2.58m (b) 2.30m (c) 3.54m (d) 2.24m

Correct choice is (a) 2.58m Easiest explanation: Force = 1N. Initial area = πr^2 = 2.82*10^-5m^2. Stress = Y*Strain Δl = F/A * l/Y = (1/2.82*10^-5)*(1/10^5) = 0.35m As volume will remain same (we can also say that product of l & r^2 will be constant as other terms in expression of volume are constants). 1*3^2 = 1.35*R^2 ⇒R = 2.58m.