In an ice hockey game a player with red T-shirt hits another player with green T-shirt. After the collision the green T-shirt player who was initially at rest moves with 2 m/s velocity. Masses of red and green T-shirt players are 40kg and 60kg respectively. Find the initial speed of the red T-shirt player?

The collision is elastic as no frictional force exists.

Both momentum and energy will be conserved.

We shall apply velocity formula applicable in respect of elastic collision

m₁ and m₂ be mass of red and green T shirt player, u₁ and u₂ be their initial velocity, v₁ and v₂ be their final velocity

v₂ = (m₂-m₁) u₂ / (m₁+m₂) + 2 m₁u₁ / (m₁+m₂)

Given m₁ = 40 kg, m₂ = 60 kg, v₂ = 2 m / s, u₁ = ?, u₂ = 0

Put the values in the equation

2 = 0 + 2 x 40 x u₁ / (40 + 60)

u₁ = 2.5 m / s.

Initial speed of red T - shirt.