Question

An object is observed from two points A and B. The object changes its position continuously with respect to A. However, the position of the object is constant with respect to B. Which of the following is/are true?

• A. The object is in motion with respect to B.
• B. The object is in motion with respect to A.
• C. The object is at rest with respect to B.
• D. The object is at rest with respect to A.

Answer 1

Answer: (B), (C)

The object is at rest with respect to B.

An object is said to be in motion when its position changes with respect to the reference point.
In this situation, there are two reference points, A and B. From the point of view of A, the object is changing its position. Hence, it's said to be in motion with respect to A.
From the point of view of B, the object is not changing its position. Hence, it's said to be at rest with respect to B.