Question

A force of 1 kgf displaces a body by a distance of 10 cm
(i) in direction of force,
(ii) normal to the force
(iii) at an angle of 60° to the direction of the force.
Calculate the amount of work done in each case. (Take: g = 9.8 ms⁻² )

Answer 1

Given : F = 1 kgf = 1 × g Newton

(i) When displacement is in direction of force.

θ = 0°, cos 0° = 1

W = F × d = 9.8 × 0.1 = 0.98 J.

(ii) When displacement is normal to the force

θ = 90°, cos 90° = 0, i.e.,W = 0.

(iii) When displacement is at an angle of 60° to the direction of force 

θ = 60° or, cos 60° =`1/2`

W = F . d cos θ = `9.8xx0.1xx1/2` = 0.49 J.