A 5000-kg freight car runs into a 10,000-kg freight car at rest. They couple upon collision and move with a speed of 2 m/s. What was the initial speed of the 5000-kg car? A) 4 m/sB) 5 m/sC) 6 m/sD) 8 m/sE) none of these

C) 6 m/s

Explanation:

Given that

m₁=5000 kg

The initial velocity of 5000 kg car = u₁

m₂=10,000 kg

The initial velocity of 10000 kg car = u₂ = 0 m/s

After collision the final speed of the both car, v = 2 m/s

There is no any external force on the system that is why linear momentum will be conserved.

Linear momentum P = m v

m₁u₁ + m₂u₂ = (m₂ + m₁) v

5000 x u₁ + 10000 x 0 = (5000 + 10000) x 2

5000 x u₁ = 15000 x 2

5 x u₁ = 15 x 2

u₁ = 6 m/s

Therefore the answer is C.

C) 6 m/s