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For a rigid body, the centre of mass moves as though the body's total mass were concentrated there and all external forces acted on it. This statement is:
AAlways true
BTrue only for non-rotating bodies
CTrue only in uniform gravity
DNot true in general
Answer & Solution
Correct answer: A. Always true
1. From Newton's second law applied to each particle and summing, internal forces cancel in pairs (third law).
2. The resultant becomes M (d²R_cm/dt²) = ΣF_ext.
3. So the centre of mass moves as if all mass were there and only external forces acted — true for ANY system of particles.
_Source: NCERT Class 11 Physics Ch 6 §6.4 CM Motion_
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