A force of 20 N displaces a body by a distance of 4 m. Find the amount of work done when the displacement is:

(a) in the direction of force.

(b) at an angle of 60° with the force.

Given,

Force (F) = 20 N

and

Displacement (s) = 4 m

(a) When displacement is in the direction of force, θ = 0°

W = Fs cos θ°

= Fs cos 0°

= 20 x 4 x 1 [∵ cos 0° = 1]

= 80 J

(b) When displacement is at an angle 60° with the direction of force,

W = Fs cos θ°

= Fs cos 60°

= 20 x 4 x $\dfrac{1}{2}$ [∵ cos 60° = $\dfrac{1}{2}$]

= 40 J