The potential energy of a certain spring when stretched through a distance S is 10 joule. The amount of work in joule) that must be done on this spring to stretch it through additional distance S will be 

Options

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

Answer

A

Explanation

`U = 1/2 kS^2 = 10 J " " …(i)`
`U. = 1/2 k (S + S)^2 = U (1/2 kS^2) = 40 J " " ` (using (i))
`:. W = U. - U = 40 J - 10 J = 30 J`.