Free JEE Main Physics Motion of COM & Reference Frames MCQs with step-by-step solutions (2 questions). Part of Centre of Mass, Momentum & Collisions. Practise online on Prepizo — no login needed.
Q1 — Motion of COM & Reference Frames · easy · numerical
Two skaters, 40 kg and 60 kg, at rest push off each other on smooth ice. Their centre of mass:
A. Remains at rest where it was ✓ Correct
B. Moves towards the lighter skater
C. Oscillates
D. Moves towards the heavier skater
Solution: The pushes are internal; with no net external horizontal force, v_cm stays zero.
Q2 — Motion of COM & Reference Frames · medium · numerical
A 1 kg and a 2 kg mass start from rest under ONLY their mutual attraction. When the 1 kg mass has speed 2 m/s, the 2 kg mass has speed:
A. 4 m/s
B. 0.5 m/s
C. 2 m/s
D. 1 m/s ✓ Correct
Solution: Momentum stays zero: 1×2 = 2×v ⇒ v = 1 m/s (towards it).