An object travelling at constant velocity implies that:

Question

BlackTom AI · Accepted Answer

Newton’s first law and Newton’s second law are the key concepts. Newton’s first law (inertia) says an object moves with constant velocity unless acted on by a net external force. Newton’s second law quantifies this: ΣF = m a, where ΣF is the net (vector) force, m is mass, and a is acceleration.

Step‑by‑step reasoning:
1. Constant velocity means the velocity vector does not change in time — both speed and direction remain constant. Therefore the acceleration a = dv/dt = 0.
2. Apply Newton’s second law: ΣF = m a. Substitute a = 0 to get ΣF = m × 0 = 0.
3. Thus the net (vector sum of all) forces acting on the object must be zero.

Intermediate steps shown:
- Given: velocity v is constant → a = 0.
- From ΣF = m a → ΣF = m × 0 = 0.

Why the correct answer is correct:
- Option a states “The net force acting on the object is zero,” which exactly matches ΣF = 0 derived above. That is the necessary and sufficient condition for motion at constant velocity in Newtonian mechanics.

Why the other options are incorrect:
- Option b (“The friction force acting on the object is zero”): Friction need not be zero; friction can be present but balanced by another force (e.g., engine thrust equals frictional drag), yielding net zero.
- Option c (“There are no forces acting on the object”): Incorrect because forces can exist but cancel each other; net force zero does not require every individual force to be zero.
- Option d (“There is a force pushing the object in the direction of the motion”): If there were an unbalanced forward force, the net force would not be zero and the object would accelerate; constant velocity requires no net forward push.

Conclusion: therefore the correct choice is a. The net force acting on the object is zero. This matches the provided answer.

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