Two 40 kg persons A and B move toward each other on a plank on a smooth horizontal floor with speeds v₁ and v₂ relative to plank. The plank moves 20 m right in 5 s. Which conditions can be possible?

Question

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: v₁=0, v₂=10 m s⁻¹; B: v₁=5, v₂=15 m s⁻¹; C: v₁=10, v₂=20 m s⁻¹; D: v₁=2, v₂=12 m s⁻¹.