Centre Of Mass
Two particles of masses 2 kg and 3 kg are placed at positions 0 m and 5 m along a straight line on a frictionless table. Where does the centre of mass of this two-particle system lie from the origin?
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About This Question
- Subject
- physics
- Chapter
- rotational motion
- Topic
- centre of mass
- Difficulty
- Easy
- Year
- 2025
Solution
Correct Answer:
3.0 m
As stated in NCERT Class 11, Chapter 7 (System of Particles and Rotational Motion), the centre of mass of a system of discrete particles along a line is the mass-weighted average of their positions, x_cm = (m₁x₁ + m₂x₂)/(m₁ + m₂). This point represents the location where the total mass of the system may be considered concentrated for translational motion. Substituting the given data: x_cm = (2 × 0 + 3 × 5)/(2 + 3) = (0 + 15)/5 = 3.0 m. The centre of mass therefore lies closer to the heavier 3 kg particle, which agrees with physical intuition. The option 2.5 m is wrong because it is the simple geometric midpoint and ignores the unequal masses. The option 2.0 m incorrectly biases the result toward the lighter mass. The option 1.5 m is far too close to the origin and does not match any correct mass weighting. A quick sanity check confirms the answer lies between 0 m and 5 m and is shifted toward the larger mass, as expected.
This easy difficulty physics question is from the chapter rotational motion, covering the topic of centre of mass. It appeared in the 2025 exam.
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