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# A2 momentum answer check! watch

1. 1. ball = 200g falls to the ground and just before striking the ground it has a speed of 5ms. It rebounds with velocity of 4ms. What is the magnitude and direction of the change in momentum.

My answer : it rebounds upwards at 0.8kgms

2. Water hose jects water in a fine jet at a rate of 250 litres per minute at a speed of 26ms. Denisty of water is 1000kgm^-3. What force is required to hold the hose steady?

3. A woman of mass 50kg stands on a boat of mass 80kg. Iinitially both are stationary. if the woman walks towards on end of the boat with a velocity of 1.2ms, with what velocity does the boat move, and which direction does it move?

My answer : it moves at 0.75ms in the opposite direction compared to the woman because of newtons third law (every action has an equal and opposite reaction)
2. (Original post by Zevo)
1. ball = 200g falls to the ground and just before striking the ground it has a speed of 5ms. It rebounds with velocity of 4ms. What is the magnitude and direction of the change in momentum.

My answer : it rebounds upwards at 0.8kgms

2. Water hose jects water in a fine jet at a rate of 250 litres per minute at a speed of 26ms. Denisty of water is 1000kgm^-3. What force is required to hold the hose steady?

3. A woman of mass 50kg stands on a boat of mass 80kg. Iinitially both are stationary. if the woman walks towards on end of the boat with a velocity of 1.2ms, with what velocity does the boat move, and which direction does it move?

My answer : it moves at 0.75ms in the opposite direction compared to the woman because of newtons third law (every action has an equal and opposite reaction)
1. No. The question is asking for the change in momentum. You have calculated just the momentum after the collision. What about before?
2. Yes.
3. Correct value and direction for velocity but you have not really explained why the velocity is the value it is, only why it is in the direction it is. Having said that, the question is not asking for an explanation.
3. (Original post by Stonebridge)
1. No. The question is asking for the change in momentum. You have calculated just the momentum after the collision. What about before?
2. Yes.
3. Correct value and direction for velocity but you have not really explained why the velocity is the value it is, only why it is in the direction it is. Having said that, the question is not asking for an explanation.
would it not be 0.2kgms then?
4. (Original post by Zevo)
would it not be 0.2kgms then?

No. Momentum is a vector. You need to include its direction (and change in direction) in the calculation.

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