# Physics - Momentum

> Source: https://ollybritton.com/notes/a-level/physics/topics/momentum/ · Updated: 2020-12-03 · Tags: physics, collisions, year-1

See also:
- [Physics - Collisions in 2D](https://ollybritton.com/notes/a-level/physics/topics/collisions-in-2d/)

##### What is the symbol symbol formula for momentum??
$$
p = mv
$$

##### What is the word formula for momentum??
$$
\text{momentum} = \text{mass} \times \text{velocity}
$$

##### What are the units for momentum??
$$
kgms^{-1}
$$

##### Two cars, $A$ and $B$ are travelling in the same direction at $30mph$ and $31mph$ respectively. What could be said about the "magnitude" of the collision??
It's the same as a $1mph$ collision.

##### Two cars, $A$ and $B$ are travelling towards each other at $30mph$ and $31mph$ respectively. What could be said about the "magnitude" of the collision??
It's a $61mph$ collision.

##### What is the Principle of the Conservation of Momentum??
The total momentum of two objects before a collision is equal to the total momentum of the two objects after a collision.

##### What is the height of the Burj Khalifa??
$$
828m
$$

##### How much does The Rock weigh, in kilograms??
$$
128kg
$$

##### How can the total momentum before and after an explosion be the same??
Momentum is a vector, each individual piece of shrapnel has a momentum that sums to zero.

##### What is the momentum of a watermelon resting on a table??
$$
0Ns
$$

##### What is the momentum of an exploding watermelon??
$$
0Ns
$$

##### For an elastic collision, what is true about momentum??
It is conserved.

##### For an elastic collision, what is true about total energy??
It is conserved.

##### For an elastic collision, what is true about kinetic energy??
It is conserved.

##### For an inelastic collision, what is true about momentum??
It is conserved.

##### For an inelastic collision, what is true about total energy??
It is conserved, but transferred.

##### For an inelastic collision, what is true about kinetic energy??
It is __not__ conserved.

### 2021-01-21
##### How should you actually define the Law of Conservation of Momentum??
In a closed system, linear momentum is conserved in both directions.

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