A block of mass 5 kg is resting on a smooth surface. At what angle a force of 20 Nbe acted on the body so that it will acquire a kinetic energy of 40 J after moving 4 m?

Options

A. `30^@`
B. `45^@`
C. `60^@`
D. `120^@`

Answer

C

Explanation

According to work-energy theorem
W=change in kinetic energy
`Fs cos theta = 1/2 mv^2 - 1/2 m u^2`
Substituting the given values, we get,
`20 xx 4 xx cos theta = 40 - 0 ( because u = 0)`
`cos theta = 40/80 = 1/2`
`theta = cos^(-1)(1/2) = 60^@`