P2 Momentum

Question 1

What is momentum?

Answer 1

momentum = mass x velocity

It is a measure of “how difficult” is is to stop something

Question 2

What are the units of momentum?

Answer 2

Momentum = mass x velocity

(kgm/s) (kg) (m/s)

Question 3

What is the law of conservation of momentum?

Answer 3

The momentum of a system after a collision is always the same as the momentum before the collision.

initial momentum = final momentum

Question 4

Can momentum be negative?

Answer 4

YES

Momentum is a vector quantity so you must have a direction.

Two equal mass cars moving at the same speed but in opposite directions will have the same size momentum but one will be positive and one will be negative.

You choose which is + and which is -

Question 5

Why does a gun recoil when it is fired?

Answer 5

1. Before firing, bullet + gun have zero momentum
2. After firing, the bullet gains momentum (it is moving)
3. Total momentum after = total momentum before
4. Bullet has positive momentum so gun must have negative momentum ie. it moves in the opposite direction