A non-zero external force acts on a particle system. At an instant, let the centre-of-mass velocity be V and centre-of-mass acceleration be A. Which cases are possible? (i) V = 0, A = 0; (ii) V ≠ 0, A = 0; (iii) V = 0, A ≠ 0; (iv) V ≠ 0, A ≠ 0.
Select all that apply

Question

A non-zero external force acts on a particle system. At an instant, let the centre-of-mass velocity be V and centre-of-mass acceleration be A. Which cases are possible? (i) V = 0, A = 0; (ii) V ≠ 0, A = 0; (iii) V = 0, A ≠ 0; (iv) V ≠ 0, A ≠ 0.

Select all that apply

G1 Physics · Accepted Answer

With zero external horizontal force, the centre of mass has constant velocity and ΣmᵢΔxᵢ = 0 in the centre-of-mass relation. Applying this to the given motion gives A: (iii) and (iv).