A spring of force constant `800N//m` has an extension of 5cm. The work done in extending it from 5cm to 15cm is

Explanation

`W = (1)/(2) K (x_(2)^(2) - x_(1)^(2)) = (1)/(2) xx 800 [15^(2) - 5^(2)] xx 10^(-4)`
`= 400xx [225-25] xx 10^(-4) = 4xx10^(-2) xx 200 = 8J`