A block of mass `m` lies on a horizontal frictionless surface and is attached to one end of a horizontal spring (with spring constant `k`) whose other end is fixed . The block is intinally at rest at the position where the spring is unstretched `(x=0)`. When a constant horizontal force `vec(F)` in the positive direction of the `x-`axis is applied to it, a plot of the resulting kinetic energy of the block versus its position `x` is shown in figure. What is the magnitude of `vec(F)` ?

Options

A. `2N`
B. `4N`
C. `8N`
D. `16N`

Answer

C

Explanation

At equilibrium, F=kx &
`Fx-(1)/(2)kx^(2)=DeltaK.E.=4`
here x=1m {i.e. mean position}