WAEC Physics 2015 Paper

Concept:Displacement is the shortest straight-line distance from the starting point to the final position.Explanation:Since the answer choices are in metres, the eastward distance is taken as $40\ \mathrm{m}$.The girl moves $40\ \mathrm{m}$ east and then $30\ \mathrm{m}$ north.These two displacements are perpendicular to each other.Therefore, the magnitude of displacement is found using Pythagoras’ theorem.Let $d$ be the displacement.Then $d = \sqrt{(40)^2 + (30)^2}$$d = \sqrt{1600 + 900}$$d = \sqrt{2500}$$d = 50\ \mathrm{m}$Answer:The magnitude of her displacement is $50\ \mathrm{m}$.Hence, the correct option is C.