A body with no net external force acts on it. Which statement best describes its motion?

A body with no net external force acts on it. Which statement best describes its motion?

• A. Remains at rest or continues moving with constant velocity
• B. Accelerates
• C. Changes momentum
• D. Loses energy

Answer: (A)

When there is no net external force, the object experiences zero acceleration. That means its velocity stays constant: if it’s at rest, it stays at rest; if it’s moving, it keeps moving in a straight line at the same speed. With constant velocity, momentum p = m v doesn’t change and the kinetic energy remains the same. The other statements would require a net force or work being done on the object, which isn’t happening here. So the motion is best described by remaining at rest or continuing with constant velocity.

When there is no net external force, the object experiences zero acceleration. That means its velocity stays constant: if it’s at rest, it stays at rest; if it’s moving, it keeps moving in a straight line at the same speed. With constant velocity, momentum p = m v doesn’t change and the kinetic energy remains the same. The other statements would require a net force or work being done on the object, which isn’t happening here. So the motion is best described by remaining at rest or continuing with constant velocity.