A certain spring that obeys Hook's law is stretched by an external agent. The work done in stretching the spring by `10 cm is 4 J` . How much additional work is required to stretch the spring an additional `10 cm`?

Options

A. 10J`
B. 20 J`
C. `30J`
D. `40 J`

Answer

C

Explanation

Potential energy of the spring when strched through a distance `x`
`U'= (1)/(2) kx^(2) = 10 J`
When `x` become `2x` the potentil enrgy will be
`U'= (1)/(2) k(2x)^(2) =4 xx (1)/(2) kx^(2) =4 xx 10= 40J`
`:.` Work done` = U'- U = 40 - 10= 30 J`