WAEC Physics 2020 Paper

Concept:Work done by a constant horizontal force is the product of the force and the distance moved in the direction of the force.Since the box moves at constant speed, the applied horizontal force equals the kinetic friction force.Explanation:Normal reaction on the box equals its weight: $R = 500\, \mathrm{N}$.Kinetic friction is $f = \mu R = 0.22 \times 500 = 110\, \mathrm{N}$.For constant motion, applied force $F = f = 110\, \mathrm{N}$.Distance moved is $s = 8\, \mathrm{m}$.Work done is $W = F s = 110 \times 8 = 880\, \mathrm{J}$.Answer:The work done on the box is $880\, \mathrm{J}$, which is option A.