If no net force acts on an object, the object maintains a state of rest or constant speed in a straight line. The above is a statement of Newton's

Step 1: Analyze the question The statement says that when no net (resultant) force acts on an object, it stays at rest or keeps moving at constant speed in a straight line. We need to match this to the correct law.

Step 2: The concept

• First law (law of inertia): An object remains at rest, or moves with uniform velocity in a straight line, unless acted on by a net external force.
• Second law: F = ma. The net force equals mass times acceleration.
• Third law: For every action there is an equal and opposite reaction.
• Law of universal gravitation: Every two masses attract each other with a force F = Gm₁m₂/r².

Step 3: Solution The statement is about what happens when the net force is zero. If F = 0, the acceleration is zero, so the velocity does not change. This is exactly the idea of inertia: objects resist changes in their state of motion.

• The second law deals with how an object accelerates when a net force acts, so it does not fit.
• The third law deals with pairs of forces between two bodies, so it does not fit.
• The law of universal gravitation deals with attraction between masses, so it does not fit.

The statement is a description of Newton's first law of motion.

Step 4: Answer A. first law of motion

Tip: Link the first law with the word inertia and with the phrase "no net force". Whenever a question says "remains at rest or moves with constant velocity unless acted upon by a force", the answer is the first law. For the second law, look for "acceleration" or "F = ma". For the third law, look for "action and reaction".