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# A2 Physics Question! OCR Unit 1 Tweet

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1. A2 Physics Question! OCR Unit 1
Okay I was given a extension question which is meant to be challenging I seem to find an answer very easily, so must be going wrong. Here it is;

QUESTION

Flour falls vertically onto a conveyor belt at a constant rate of .

The conveyor belt is moving at a constant speed of .

Calculate the horizontal force required to keep the belt moving.

MY WORKING

Therefore

So

Which ends up with this challenging question only being

Last edited by Amy-Chod; 27-06-2012 at 18:27.
2. Re: A2 Physics Question! OCR Unit 1
The question states 3kg per second but you have used 3.2 kg per sec in the calculation.

What is the answer given as "correct"?

Why have you multiplied those two figures together? You would need to justify this method and state the principle on which it is based.
3. Re: A2 Physics Question! OCR Unit 1
(Original post by Stonebridge)
The question states 3kg per second but you have used 3.2 kg per sec in the calculation.

What is the answer given as "correct"?

Why have you multiplied those two figures together? You would need to justify this method and state the principle on which it is based.
Sorry updated the question, Thanks
4. Re: A2 Physics Question! OCR Unit 1
The "challenge", I suspect, is to explain why your method gives the answer.
Yes, it's about momentum. It's about force being equal to "rate of change of momentum", or "change of momentum per second".
You haven't explained what, exactly, you mean by "initial" and "final" velocity.
I could say that the flour is falling from a height, and so has an initial and final vertical velocity.
You need to make it clear
1. which velocities you are talking about.
2. that you are using rate of change of momentum.
3. that the mass per second x velocity gives rate of change of momentum
4. that the relevant momentum is horizontal and not vertical
5. that because the belt is moving at constant velocity there no resultant force needed to move it if you ignore friction, and the only force required is the one to change the horizontal momentum of the flour.

The numerical calculation is simple, but your first attempt looked like a guess. This would lose marks marks in an extension question.
The second attempt is better but you have not correctly explained the principles you applied.

Hope this helps.
Last edited by Stonebridge; 28-06-2012 at 08:08.
5. Re: A2 Physics Question! OCR Unit 1
(Original post by Amy-Chod)
Okay I was given a extension question which is meant to be challenging I seem to find an answer very easily, so must be going wrong. Here it is;

QUESTION

Flour falls vertically onto a conveyor belt at a constant rate of .

The conveyor belt is moving at a constant speed of .

Calculate the horizontal force required to keep the belt moving.

MY WORKING

Therefore

So

Which ends up with this challenging question only being