Momentum and Collisions

Question 1

What is the equation for momentum?

Answer 1

Momentum = mass x velocity

Question 2

What is the sign for momentum?

Answer 2

p

Question 3

Momentum is a property of what?

Answer 3

Moving objects

Question 4

What happens to momentum as the mass is increased?

Answer 4

The momentum increases too

Question 5

What happens to momentum when the velocity increases?

Answer 5

The momentum increases too

Question 6

What does it mean that momentum is a ‘vector’ quantity?

Answer 6

It measures size and direction

(like velocity, but not speed)

Question 7

What is the formula triangle for momentum?

Answer 7

Question 8

Write the units in the momentum equation

Answer 8

momentum (kgm/s) = mass (kg) x velocity (m/s)

Question 9

What is the equation for momentum before and after a collision? (in a closed system)

Answer 9

Momentum before = Momentum after

Question 10

What is the fact that momentum after a collision is equal to the momentum before the collision known as?

Answer 10

Conservation of Momentum

Question 11

State the steps in answering a momentum question in a collision (asking for the velocity)

Answer 11

1. Choose which direction is positive (e.g. to the right)
2. Work out total momentum before collsion by adding the momentum of the 2 colliding objects
3. Add the masses of the objects, and arrange in this formula:

total momentum = combined masses x velocity

4. you should be able to rearrange the equation to get the velocity (as you have the figures of the underlined parts)

Question 12

Try a practice question:

Two ice hockey players are skating towards the puck. Player A has a mass of 100kg and is travelling right at 6 m/s. Player B has a mass of 80kg and is travelling left at 9m/s.

Calculate the momentum of:

a) Player A
b) Player B

Answer 12

momentum = mass x velocity

right = positive

a) Player A: 100 kg x 6 m/s = 600 kgm/s to the right
b) Player B: 80kg x -9 m/s = 720 kgm/s to the left ( -720 kgm/s )

Question 13

The second part to the question:

(Player A’s momentum = 600 kgm/s, mass = 100 kg, and Player B’s momentum = -720 kgm/s, mass = 80 kg)

The two players collide and become joined together.

a) Calculate the speed of the 2 joined players just after the collision
b) State the direction they move

Answer 13

momentum = mass x velocity

right still = positive (although you could change this)

a) 600 kgm/s + - 720 kgm/s = -120
- 120 = (100 + 80) x v
- 120 = 180 x v
- 120 / 180 = v = -0.666… = -0.67 m/s
b) They move to the left