The work done by the external agent in stretching a spring of force constant `k` from length `l_(1)`to `l_(2)` is

Options

A. `k(l_(2)^(2) - l_(1)^(2))`
B. `(1)/(2)k(l_(2)^(2) - l_(1)^(2))`
C. `k(l_(2) - l_(1))`
D. `k//2(l_(2) - l_(1))`

Answer

B

Explanation

`U_(2) = (1)/(2)Kl_(2)^(2)`
` U_(1) = (1)/(2)Kl_(2)^(2)`
`W=U_(2) - U_(1)`
`(1)/(2)Kl_(2)^(2)- (1)/(2)Kl_(1)^(2) = (1)/(2)K(l_(2)^(2)- l_(1)^(2))`