Year 12s: what will be the first way you research your future options? >>

P2.3.4 - Momentum Question

AlphaMolecule

removed

(edited 9 years ago)

Reply 1

uberteknik

Original post by AlphaNick

3 - The diagram below shows two tows cars of identical mass travelling towards each other. The car on the left has a mass of 0.2kg and a speed of 5m/s.

a) What is the value of the momentum of the car on the left?

b) The momentum of the car on the right is 1.5 times larger than the momentum of the other car, what is the total momentum before they collide?

Before getting to your answer, we need to understand the question first.

The way the question is worded between that which you typed and that written in the scan, raises ambiguity: if the momentum of the car on the right is 1.5x that of the car on the left and the mass of each car is 0.2kg, then the speed of each car before the collision cannot be the same. i.e. both cars cannot be travelling at 5m/s.

So reading the question text written on the attached scan, that would imply the closing speed of the cars is 5m/s and not 5m/s each.

But that means part a) cannot be answered without first taking into account the information provided in part b).

Have you copied the question exactly as it's written in your extension sheet, or have you made assumptions or possibly missed a word or two?

Would be good if you could scan and post the full question please?

(edited 10 years ago)

Reply 2

uberteknik

Original post by AlphaNick

I copied out the questions exactly was they were written.

And I didn't assume that both cars would be travelling at 5m/s... In part C I worked out using the momentum that it would be travelling at 7.5m/s.

I've attached the sheet.

Thanks for that.

I do beg to differ though.

There are two questions on the toy cars in the paper you posted, and neither question asks for:

a) the value of the momentum of the car on the left.
It does ask for 'The value of the momentum of each car.'

Neither question states

b) the momentum of the car on the right is 1.5x larger than the other car.

Neither question asks

c) what is the speed of the car on the right?

Sooooo......

Was this question modified by your teacher by stating the momentums of the cars differ by 1.5x?

I'm not having a go, and we can work through both examples i.e. a) as it's written on the paper and b) by making some assumptions as per my original post and answering it as per your copied wording.

Either way is not a problem. :smile: