A particle is projected from point P with velocity 5√3 ms⁻¹ perpendicular to the surface of a hollow right angled cone as shown in figure. It collides at Q normally. The velocity with which it collides at Q will be

Question

G1 Physics · Accepted Answer

The right-hand surface is at 30° to the horizontal, so a velocity normal to it is at -60°. The left surface is perpendicular to the right surface; therefore the initial velocity normal to the left surface is at +30°. Initial horizontal component = 5√3 cos30° = 15/2 m/s and remains constant. At Q, if impact speed is V, its horizontal component is V cos60° = V/2. Thus V/2 = 15/2 and V = 15 m/s. Hence option B.