# A railway car with a mass of 20 tons, moving along a horizontal track at a speed of 10 m / s, collides with a stationary platform

**A railway car with a mass of 20 tons, moving along a horizontal track at a speed of 10 m / s, collides with a stationary platform with a mass of 5 tons. At what speed will the car and the platform move after the coupler is triggered?**

To find the value of the speed of the joint movement of the platform and the railway carriage, we use the equality (we apply the law of conservation of momentum): Vw * mw + Vp * mp = V * (mw + mp), from where we express: V = (Vw * mw + Vp * mp) / (mv + mp).

Variables: Vв – the speed of the car before the automatic coupling (Vв = 10 m / s); mw is the mass of the car (mw = 20 t); Vп – platform speed to automatic coupling (Vп = 0 m / s); mp – platform weight (mp = 5 t).

Calculation: V = (Vw * mw + Vp * mp) / (mw + mp) = (10 * 20 + 0 * 5) / (20 + 5) = 200/25 = 8 m / s.

Answer: After the automatic coupling, the platform and the car will move at a speed of 8 m / s.