A car weighing 20 tons moves at a speed of 7.5 m / s and collides with three stationary

A car weighing 20 tons moves at a speed of 7.5 m / s and collides with three stationary cars, each weighing 10 tons. What is the speed of their joint movement?

To solve this problem, we use the law of conservation of momentum. Let’s use the formula. Where M1 = 20 t is the mass of the moving car. Where V1 = 7.5 m / s – the speed of the moving car. Where M3 = 30 t is the mass of three stationary cars. After the collision of the cars, the total momentum is preserved and equal.

M1 * V1 = M1 * V2 + M3 * V2 = (M1 + M3) * V2.

From here we find a new speed after the collision of the cars.

V2 = M1 * V1 / (M1 + M3) = (20 t * 7.5 m / s) / (20 t + 30 t) = 150/50 = (3 m / s).

Answer: the speed is V2 = (3 m / s).