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.

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