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

Options

A. 84 J
B. 68 J
C. 23 J
D. 8 J

Answer

D

Explanation

x = 40 mm
if x = 1 mm, F = 10 N
Since F = kx
`implies k = F/ x = 10/(0.001) = 10^4 N//m`
`W =1/2 kx^2 =1/2 xx10^(4) xx (40)^2 xx10^(-6) = 8J`