WAEC Physics 2014 Paper

Concept:Newton's first law of motion is also called the law of inertia: an object will not change its state of motion unless a net external force acts on it.Explanation:The given statement exactly describes this law.When no net force acts on an object, the net force is $F_{\text{net}} = 0$.From Newton's second law, $F_{\text{net}} = ma$, so $0 = ma$, which gives $a = 0$.Zero acceleration means the velocity of the object is constant.Constant velocity includes two cases: the object is at rest, or the object moves with constant speed along a straight line.Therefore, the object maintains its state of rest or uniform straight-line motion.Newton's first law of motion is the law that states this property of inertia.The first law is the correct match for the statement.Answer:A. first law of motion