Q. Two bodies of mass 1 kg and 3 kg have position vectors î + 2ĵ + k̂ and −3î − 2ĵ + k̂, respectively. The centre of mass of this system has a position vector:
A) −2î − ĵ + k̂
B) 2î − ĵ − 2k̂
C) −î + ĵ + k̂
D) −2î + 2k̂
Explanation
[Solution from source] r_cm = (m₁r₁ + m₂r₂)/(m₁ + m₂) = [(î + 2ĵ + k̂) + 3(−3î − 2ĵ + k̂)]/4 = (−8î − 4ĵ + 4k̂)/4 = −2î − ĵ + k̂. Answer (1).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.