Conservation of linear momentum: If we calculate the momentum of each object **before** a collision, it should **equal** the total vector sum of the momentum of the objects** afterwords**. This depends on the **condition that no external force** is added.

**This is directly responsible for Newtons 3rd Law**

Explosions: If a stationary object 'explodes', then the total momentum of all the shrapnel parts must be zero. Zero momentum initially = Zero momentum after.

Calculating momentum in two dimensions requires resolving of vectors.

- First calculate total
**horizontal** momentum before collision, including both objects.
- Then calculate the total momentum
**vertically** of the two objects before the collision.
- Using
**Pythagoras theorem**, we can work out **P-total after collision**. in the actual direction.
- For angle of momentum afterwards (i.e direction of velocity) use tan-1(total vertically/total horizontally).

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