When forming a train, three coupled cars moving at a speed of 0.4 m / s collide with a stationary car

When forming a train, three coupled cars moving at a speed of 0.4 m / s collide with a stationary car, after which all cars continue to move in the same direction. Find the speed of the cars if all cars have the same mass.

Data: V1 (coupling speed of three cars) = 0.4 m / s; m (wagon mass) = m1 = m2 = m3 = m4; V2 (speed of the fourth car before coupling) = 0 m / s.

To determine the speed of a coupling of four cars, we apply the law of conservation of momentum: V1 * 3m + V2 * m = V * 4m, whence V = (V1 * 3m + V2 * m) / 4m = (V1 * 3m + 0) / 4m = 3V1 / 4.

Calculation: V = 3 * 0.4 / 4 = 0.3 m / s.

Answer: After coupling, four cars will move at a speed of 0.3 m / s.