A body weighing 20 kg moves at a speed of 72 km / h and adheres to a body weighing 30 kg

A body weighing 20 kg moves at a speed of 72 km / h and adheres to a body weighing 30 kg, which moves at a speed of 10 m / s. Find their overall speed if the bodies A) move in the same direction, B) move towards each other.

Given:

m1 = 20 kg is the mass of the first body;

m2 = 30 kg – the mass of the second body;

V1 = 72 km / h = 20 m / s – the speed of the first body;

V2 = 10 m / s is the speed of the second body.

It is required to find the overall speed V3 during adhesion, if the bodies move in the same direction and towards each other.

According to the law of conservation of momentum:

if the bodies are moving in one direction:

V3 = (m1 * v1 + m2 * v2) / (m1 + m2) = (20 * 20 + 30 * 10) / (20 + 30) = 700/50 = 14 m / s.

if the bodies are moving in opposite directions:

V3 = (m1 * v1 – m2 * v2) / (m1 + m2) = (20 * 20 – 30 * 10) / (20 + 30) = 100/50 = 2 m / s.

Answer: the total speed will be equal to 14 m / s when moving in one direction, and 2 m / s when moving towards each other.