What is the shape of the graph between speed and kinetic energy of a body?

A quarter horse power motor runs at a speed of 600 rpm. Assuming 60% efficiency, the work done by the motor in one rotation is

A body of mass 8 kg, under the action of a force, is displaced according to the equation, $$s=\frac{t^2}{4}$$ m, where t is the time. Find the work done by the force in the first 4 s.