WAEC Physics 2019 Paper

Concept:Newton's laws of motion relate resultant force to acceleration, not to motion itself.Explanation:A moving object may travel at a steady velocity, which means its acceleration is zero.According to Newton's first law, when the resultant force acting on an object is zero, the object continues moving with constant velocity.According to Newton's second law, $F_{\text{net}} = ma$.If acceleration is zero, then $F_{\text{net}} = 0$.Therefore, at a steady velocity, the resultant force acting on the object must be zero.Option A is incorrect because acceleration requires a non-zero resultant force, not a zero resultant force.Option B is incorrect because constant motion can occur without any resultant force.Option D is incorrect because air resistance can be present as long as it is balanced by other forces, giving a zero resultant force.Answer:C. At a steady velocity, the resultant force acting on it must be equal to zero.