If the net external force acting on a mass is zero, what will be its motion?

• A. Constant velocity (the object could be at rest or moving in a straight line with constant speed).
• B. Increasing velocity over time.
• C. Accelerating downward due to gravity.
• D. Following a circular path.

Answer: (A)

When there is no net external force on an object, its motion doesn’t change. This is Newton’s first law: an object at rest stays at rest, and an object in motion continues moving in a straight line at constant speed unless something else acts on it. If the mass is at rest, it remains at rest; if it’s already moving, it keeps moving with the same speed in a straight path. Only a net force can change that state.

Increasing velocity would require a net force to speed it up, accelerating downward implies a net downward force, and following a circular path requires a net inward (centripetal) force. So the motion remains constant velocity.