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P5: Quiz 21 – Answers

P5: Quiz 21 – Answers

1) p = mv or momentum = mass x velocity

momentum is measured in kilogram metres per second (kg m/s), mass is measured in kilograms (kg) and velocity is measured in metres per second (m/s)

momentum is measured in kilogram metres per second (kg m/s), mass is measured in kilograms (kg) and velocity is measured in metres per second (m/s)

2) The law of conservation of momentum states that the momentum before an event is equal to the momentum after an event. The event can either be a collision or an explosion

3)

a)

i) 136.8 kg m/s towards the right

ii) 0 kg m/s

iii) 136.8 kg m/s towards the right

b)

i) 136.8 kg m/s towards the right

ii) 90 kg

iii) 1.52 m/s towards the right

c)

i) The velocity of Alexandra decreases during the collision; before the collision her velocity was 3.6 m/s and after the collision her velocity is 1.52 m/s

ii) The velocity of Betty increases during the collision; before the collision her velocity was 0 m/s as she was stationary and after the collision her velocity is 1.52 m/s

4)

a) 36 kg m/s

b) 36 kg m/s

c) 0.36 m/s towards the right

5)

a) 0 kg m/s

b) 0 kg m/s

c) 480 m/s (towards the right)

6) 0.52 m/s towards the left

**Questions**

1) Write down the equation for momentum. Give the units for all of the variables.

2) What is the law of conservation of momentum?

3) We have two skaters; Alexandra and Betty. Alexandra has a mass of 38 kg and a velocity of 3.6 m/s towards the right. Betty has a mass of 52 kg and is stationary. The diagram below shows some of the key details.

Alexandra crashes into Betty. After the collision, they grab onto each other and move towards the right.

a)

i) Calculate the momentum of Alexandra before the collision.

ii) Calculate the momentum of Betty before the collision.

iii) Calculate the total momentum before the collision.

b)

i) What is the momentum after the collision?

ii) What is the total mass when they grab onto each other after the collision?

iii) Calculate the velocity of the individuals joined together after the collision. Give the direction of travel as well.

c)

i) Describe what happens to the velocity of Alexandra before and after the collision.

ii) Describe what happens to the velocity of Betty before and after the collision.

4) We have two skaters; Charlotte and Daisy. Charlotte has a mass of 42 kg and a velocity of 5 m/s towards the right. Daisy has a mass of 58 kg and a velocity of 3 m/s towards the left. The diagram below shows some of the key details.

a)

i) Calculate the momentum of Alexandra before the collision.

ii) Calculate the momentum of Betty before the collision.

iii) Calculate the total momentum before the collision.

b)

i) What is the momentum after the collision?

ii) What is the total mass when they grab onto each other after the collision?

iii) Calculate the velocity of the individuals joined together after the collision. Give the direction of travel as well.

c)

i) Describe what happens to the velocity of Alexandra before and after the collision.

ii) Describe what happens to the velocity of Betty before and after the collision.

4) We have two skaters; Charlotte and Daisy. Charlotte has a mass of 42 kg and a velocity of 5 m/s towards the right. Daisy has a mass of 58 kg and a velocity of 3 m/s towards the left. The diagram below shows some of the key details.

Charlotte and Daisy crash into each other. After the collision, they grab onto each other and both travel in the same direction.

a) Calculate the total momentum before the collision. Take your momentum towards the right.

b) Calculate the total momentum after the collision. Take your momentum towards the right.

c) Calculate the velocity of Charlotte and Daisy after the collision. Make sure that you give the direction of travel.

5) The next question involves a gun and a bullet. The gun has a mass of 600 grams and the bullet has a mass of 50 grams.

a) Calculate the total momentum before the collision. Take your momentum towards the right.

b) Calculate the total momentum after the collision. Take your momentum towards the right.

c) Calculate the velocity of Charlotte and Daisy after the collision. Make sure that you give the direction of travel.

5) The next question involves a gun and a bullet. The gun has a mass of 600 grams and the bullet has a mass of 50 grams.

When the gun is fired, the gun recoils to the left with a velocity of 40 m/s and the bullet travels towards the right.

a) What is the total momentum before the gun is fired?

b) What is the total momentum after the gun is fired?

c) Calculate the velocity at which the bullet is fired out at.

6) We have a boat with an individual on; both the boat and the individual are stationary. The boat has a mass of 295 kg and the individual has a mass of 55 kg.

The individual dives off of the boat towards the right with a velocity of 2.8 m/s.

a) What is the total momentum before the gun is fired?

b) What is the total momentum after the gun is fired?

c) Calculate the velocity at which the bullet is fired out at.

6) We have a boat with an individual on; both the boat and the individual are stationary. The boat has a mass of 295 kg and the individual has a mass of 55 kg.

The individual dives off of the boat towards the right with a velocity of 2.8 m/s.

Calculate the velocity of the boat and give the direction that the boat moves in. Give your answer to 2 significant figures.