Newton's first law states that an object at rest stays at rest, and an object in motion continues at constant velocity, UNLESS:
AIt is observed
BTime passes
CAn unbalanced (net) external force acts on it
DIt is heavy
Answer & Solution
Correct answer: C. An unbalanced (net) external force acts on it
Newton's first law (law of inertia): an object's state of motion changes only if there is an unbalanced external force. With zero net force, velocity stays constant (which includes zero velocity = at rest). This is why we keep moving forward when a bus stops suddenly (inertia).
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