From Newton's first law of motion,

1. Analyze the question You're asked what follows from Newton's first law of motion, so we need to find the statement that matches the law.

2. Explain the concept Newton's first law (the law of inertia) says:

> A body remains at rest, or continues in uniform motion in a straight line, unless acted upon by a resultant (net) external force.

The key idea is net force. If the net force is zero, the velocity doesn't change: a body at rest stays at rest, and a body moving at constant velocity keeps moving at constant velocity.

3. Check each option

• A. A body can only undergo translational motion. Wrong. Bodies can also rotate or vibrate. The first law doesn't say this.
• B. Once a body remains at rest no force acts on it. Wrong. A book on a table is at rest, yet its weight and the normal reaction both act on it. What is true is that the net force is zero, not that no force acts.
• C. The net force acting in uniform linear motion is zero. Correct. Uniform linear motion means constant velocity, so there is no acceleration. By the first law (and F = ma with a = 0), the resultant force must be zero.
• D. A body's inertia is its weight. Wrong. Inertia is a body's tendency to resist a change in its state of motion, and it is measured by mass, not weight. Weight is the pull of gravity on the body (W = mg).

4. Answer The correct option is C.

5. Exam tip When you see "Newton's first law", think "net force = 0 ⟺ no change in velocity". Watch out for options that say "no force acts", because the correct wording is "net or resultant force is zero". Also remember: inertia ↔ mass, not weight.