Question

A rubber ball with a speed of 5.0 m/s collides head-on elastically with an identical ball at rest. What is the
speed of the initially stopped ball after the collision?
(A) zero
(B) 1.0 m/s
(C) 2.5 m/s
(D) 5.0 m/s
​

Answer 1

The  speed of the initially stopped ball after the collision is (D) 5.0 m/s.

- It is given that

Initial velocity of 1st rubber ball, u₁ = 5 m/s

Initial velocity of 2nd rubber ball, u₂ = 0 m/s

Masses of balls, m₁ = m₂ = m

- Since it is a head on elastic collision, so we can calculate the final velocity of second ball as :

v₂ = 2m₁u₁ / (m₁ + m₂)

v₂ = 2 × m × 5 / (m + m)

v₂ = 10 × m / 2m

v₂ = 10 / 2 = 5 m/s