A particle is found to be at rest when observed from a reference frame S1 and the same particle is found to move with a constant velocity when observed from another frame S2. Which of the following statements is true?

Correct option is D

The correct answer is (d) Both S1 and S2 are inertial frames.

Explanation:

An inertial frame of reference is one in which a body remains at rest or moves with constant velocity unless acted upon by a force (Newton's First Law holds).

• If a particle is at rest in frame S1, then S1 is an inertial frame (assuming no external forces act on the particle).

• If another frame S2 moves with constant velocity relative to S1, then the particle will appear to move with constant velocity in S2.

• By definition, any frame moving with constant velocity relative to an inertial frame is also an inertial frame.

• Therefore, both frames have zero acceleration, so both are inertial frames.

Information Booster:

• A non-inertial frame is an accelerated frame, such as:

  • a rotating platform

  • a braking or accelerating car

• In non-inertial frames, pseudo-forces (like centrifugal force) must be introduced.

Additional Knowledge:

S1 is inertial but S2 is non-inertial (Option a) is incorrect because if S2 were non-inertial, the particle would appear to have acceleration, not constant velocity.

So, the correct answer is (d).