WAEC Physics 2020 Paper

Concept:The normal force is the perpendicular component of the weight on an inclined plane.Explanation:The weight of the ball, $mg$, acts vertically downward.On a plank inclined at angle $\theta$ to the horizontal, this weight is resolved into two components.The component perpendicular to the plank is $mg\cos\theta$.The component parallel to the plank is $mg\sin\theta$.The normal force balances the perpendicular component.Kinetic friction $F$ acts along the plank and does not affect the normal force.Hence, the normal force on the ball is $R = mg\cos\theta$.Answer:C. $mg\cos\theta$