A hockey puck of mass slides across a perfectly frictionless horizontal rink at…
PHYSICS · Single correct · CBSE · Physics · Force and Laws of Motion · Force and Laws of Motion
Problem
A hockey puck of mass 0.17kg slides across a perfectly frictionless horizontal rink at constant speed. Earth’s gravity pulls downward on the puck while the rink’s surface exerts an equal upward normal force. Which statement best explains why the puck’s horizontal velocity remains constant as it moves across the ice?
(a) With no friction present, no forces act on the puck in any direction, so it continues moving at constant speed.
(b) The downward weight is balanced by the upward normal force, so there is no net force in the horizontal direction; with zero horizontal net force, the puck’s horizontal velocity stays constant.
(c) Newton’s third law pairs the weight and normal force, so every force has an opposite partner and the puck’s speed therefore cannot change.
(d) The normal force has a small forward component that pushes the puck along, exactly balancing the pull of gravity.