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

A block of mass 5 kg is resting on a smooth surface. At what angle a f

1.	A block of mass 5 kg is resting on a smooth surface. At what angle a force of 20 N be acted on the body so that it will acquired a kinetic energy of 40 J after moving 4 m?
Answer» `30^@` `45^@` `60^@` `120^@` Solution :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 "" ( :. u = 0)` or `cos theta = 40/80 = 1/2` or `theta = cos^(-1)(1/2) = 60^@` .