# Momentum

AQA A - Notes on momentum

- Created by: Amy
- Created on: 03-01-13 12:53

First 189 words of the document:

PHY4A

Momentum

If a body of mass m has a velocity v, then its momentum is

=mv

The units of momentum are kgms¯¹ or Newton Seconds (Ns)

Momentum is a vector quantity so it has a direction.

Law of conservation of momentum

Momentum is conserved in all collisions, explosions and interactions. There are no exceptions.

When two objects collide, the changes in their momenta will be equal in size but opposite in

direction. The momentum gained by one body equals the momentum lost by the other.

Tackling problems:

1. Choose which direction is positive

2. Draw before and after sketches of the objects

3. Calculate every momentum you can

4. Apply the law of conservation of momentum for collisions involving 2 bodies.

Recoil and explosions

Guns and cannons recoil when fired because of the law of conservation of momentum. The positive

momentum gained by the bullet or cannon ball is equal to the negative recoil momentum of the gun

or cannon, and so the total momentum before and after the explosion is zero.

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