If a force acting on a body has a component in the direction of displacement, then the work done by the force is positive. Hence when a body falls freely under the influence of gravity the work done by the gravity is positive.

If a force acting on a body has a component in the opposite direction of displacement, the work done is negative, when a body slides against a rough horizontal surface, its displacement is opposite to that of the force of friction. He works done by the friction is negative.

For a body moving in a circular path, the centripetal force and the displacement are perpendicular to each other. So the work done by the centripetal force is zero.

F = 20kg wt = 20×9.8N
s = 20m
θ = 60°
W = Fscosθ = 20×9.8×20×cos⁡60°
W = 1960J.

F = 10N, s = 5m, θ = 90°
Work done, W₁=Fscosθ = 10×5×cos90° = 0
For vertical motion, the angle between force and displacement is 0°.
Here, F = 10N, s = 10m, θ=0°
Work done, W₂=10×10×cos0 = 100J
Total work done = W₁+W₂ = 100J.