# A car weighing 30 tons, moving at a speed of 0.3 m / s, hits a stationary car weighing 10 tons.

**A car weighing 30 tons, moving at a speed of 0.3 m / s, hits a stationary car weighing 10 tons. What is the speed of the wagons after impact?**

m1 = 30 t = 30,000 kg.

V1 = 0.3 m / s.

m2 = 10 t = 10000 kg.

V2 = 0 m / s.

V -?

The system of two cars can be considered closed, since they interact only with each other. When the cars interact, the impulse conservation law is valid: the sum of impulses before the impact is equal to the sum of impulses after the impact.

m1 * V1 + m2 * V2 = (m1 + m2) * V.

V = (m1 * V1 + m2 * V2) / (m1 + m2).

Since the second car was immovable before the impact, the formula will be simplified: V = m1 * V1 / (m1 + m2).

V = 30,000 kg * 0.3 m / s / (30,000 kg + 10,000 kg) = 0.225 m / s.

Answer: after the impact, the cars will move at a speed of V = 0.225 m / s.