An object travelling at constant velocity implies that:

Question

BlackTom AI · Accepted Answer

Newton's first law (and Newton's second law) provide the key concept: if velocity is constant then acceleration is zero, and therefore the net force is zero.

1) Relevant knowledge points and concepts
- Velocity constant ⇒ acceleration a = 0 (velocity does not change in magnitude or direction).
- Newton's second law: F_net = m · a. If a = 0 then F_net = 0.
- “Net force = 0” does not imply there are no forces; it means all forces sum (vectorially) to zero (they can cancel).

2) Step-by-step reasoning
- Constant velocity means dv/dt = 0, so a = 0.
- Apply F_net = m · a. Substitute a = 0 to get F_net = m · 0.
- Therefore F_net = 0.

3) Calculational intermediate steps
- a = 0
- F_net = m × a = m × 0 = 0

4) Why the correct answer is correct
- Option d states “The net force acting on the object is zero,” which matches the direct consequence of a = 0 via F_net = m a. That is the precise physical condition for unchanged velocity.

5) Why the other options are incorrect
- a. “There is a force pushing the object in the direction of the motion” is not required; a forward push would cause acceleration unless balanced by an opposing force.
- b. “There are no forces acting on the object” is too strong: there can be multiple forces (e.g., thrust and drag) that cancel, so forces may be present even though their sum is zero.
- c. “The friction force acting on the object is zero” is unnecessary; friction can be nonzero but balanced by another force (e.g., engine thrust), producing zero net force.

6) Conclusion
- By Newton’s laws, constant velocity ⇒ a = 0 ⇒ F_net = 0. This confirms answer d.

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