Law of conservation
of momentum

Explanation:

Law of conservation of momentum is applied in solving collision problem. When two body collides, their momentum after collision can be determined using the law.

The law States that the sum of momentum of two bodies before collision is equal to the sum of their momentum after collision. Before collision, both bodies moves with a different velocity while during some cases, the bodies moves with a common velocity after collision.

Whether they move with or without the same velocity depends on the type of collision that exists between them after the collision. After collision, some object sticks together and move with a common velocity while some doesn't.

If the bodies sticks together after collision, the type of collision that occur is inelastic (energy is not conserved) and if they splits after collision, the type of collision that occur is an elastic collision (energy is conserved).

Let m1 and m2 be the masses of the bodies

u1 and u2 be their velocities before collision

v1 and v2 be their velocities after collision.

According to the law;

m1u1 + m2u2 = m1v1 + m2v2

Note that momentum = mass × velocity of the body.

d.7.5cm is your answer