Question

A spring 40mm long is stretched by the acceleration of a force. If 10N force is required to stretch the spring through 1mm, then work done in stretching through 40mm is?

(a) 84J

(b) 48J

(c) 24J

(d) 8J

Answer 1

Right answer is (d) 8J

For explanation: k=F/x=10N/1mm=10N/(10^-3m)=(10^4)N/m

Work done in stretching the spring through 40mm,

W=1/2×kx^2=1/2×10^4×0.04×0.04=8J.