JAMB Physics 2019 Paper

Concept:Momentum depends on mass and velocity, and velocity changes in direction during circular motion.Explanation:In uniform circular motion, the car’s speed remains constant.But velocity is a vector, so its direction continuously changes as the car moves around the track.Momentum is calculated as $p = mv$.Since mass $m$ and speed $v$ are not zero, the magnitude of momentum $mv$ is never zero.However, the direction of momentum is along the instantaneous velocity, which is tangent to the circle.At different positions, this tangent direction changes, so the momentum can point in opposite directions.Thus the momentum may be positive at one point and negative at another point with respect to a chosen reference direction.It is not zero because of its position or inertia.It is also not a centrifugal quantity.Answer:Option A — the momentum can be both positive and negative.