Newton’s laws — identify the first law statement Which of the following correctly states Newton’s first law of motion (law of inertia)?

Introduction / Context:
Newton’s three laws form the backbone of classical mechanics. The first law defines inertia and establishes that acceleration requires a net external force. Distinguishing the wording of each law prevents conceptual mix-ups in problem solving.

Given Data / Assumptions:

• Idealized point mass.
• No net external force implies constant velocity (which includes rest).

Concept / Approach:
First law (inertia): without a net external force, a body’s velocity remains constant in magnitude and direction. Second law: ΣF = m * a (rate of change of momentum proportional to applied force). Third law: action–reaction pairs equal in magnitude and opposite in direction on different bodies.

Step-by-Step Solution:
Scan options to match the law of inertia.Option (a) states precisely that velocity remains constant unless acted on by an external force.Hence, select option (a) as Newton’s first law.

Verification / Alternative check:
In the absence of resultant force, from ΣF = m * a, we have a = 0, which means velocity is unchanged—consistent with the first law’s qualitative statement.

Why Other Options Are Wrong:

• (b) describes Newton’s second law.
• (c) describes Newton’s third law.
• (d) is false because (a) is correct.

Common Pitfalls:

• Equating “no force” with “body must be at rest.” No net force implies constant velocity, which could be nonzero.

Final Answer:
every body continues in its state of rest or of uniform motion, in a straight line, unless it is acted upon by some external force