Three persons A, B and C move along a straight line with constant different speeds as shown. When B catches C, the separation between A and C becomes 4d. The speed of B is:

Question

G1 Physics · Accepted Answer

From the figure, A moves at 5 m s⁻¹ and C at 10 m s⁻¹; initially A-B and B-C are each d. When B catches C, A-C separation grows from 2d to 4d, so (10-5)t=2d ⇒ t=2d/5. Also (vᵦ-10)t=d, giving vᵦ-10=5/2 and vᵦ=12.5 m s⁻¹. Hence option C.