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M1 Momentum help

Hi all

http://filestore.aqa.org.uk/subjects/AQA-MM1B-QP-JAN13.PDF
Q(5)

MS: http://filestore.aqa.org.uk/subjects/AQA-MM1B-W-MS-JAN13.PDF


If anybody could help me with this question it'd be great.

I am understanding that it is using speed instead of velocity as a way of indicating that the speeds could be positive or negative and therefore hence the two answers. But in the question it says A and B are moving towards each other before they collide so surely one should be negative and one positive?
Original post by Rabadon
Hi all

http://filestore.aqa.org.uk/subjects/AQA-MM1B-QP-JAN13.PDF
Q(5)

MS: http://filestore.aqa.org.uk/subjects/AQA-MM1B-W-MS-JAN13.PDF


If anybody could help me with this question it'd be great.

I am understanding that it is using speed instead of velocity as a way of indicating that the speeds could be positive or negative and therefore hence the two answers. But in the question it says A and B are moving towards each other before they collide so surely one should be negative and one positive?


Yes one is positive and the other is negative. But the velocity of A after the collision could be ±0.6ms−1\pm0.6ms^{-1}
Reply 2
Avatar for Rabadon
Rabadon
OP
11
Original post by lizard54142
Yes one is positive and the other is negative. But the velocity of A after the collision could be ±0.6ms−1\pm0.6ms^{-1}


Ah, having read the MS. they've taken the B prior to the collision to have negative velocity each time. Just wondering, why haven't they used A as negative velocity at any point? Surely A could be travelling towards B with B going "to the right" as it were, and A "to the left". Or for these sort of questions do we always assume A is to the left of B? idk
Original post by Rabadon
Ah, having read the MS. they've taken the B prior to the collision to have negative velocity each time. Just wondering, why haven't they used A as negative velocity at any point? Surely A could be travelling towards B with B going "to the right" as it were, and A "to the left". Or for these sort of questions do we always assume A is to the left of B? idk


You could consider A to be negative if you'd like. It doesn't matter, but then B would be positive.
Reply 4
Avatar for Rabadon
Rabadon
OP
11
Original post by lizard54142
You could consider A to be negative if you'd like. It doesn't matter, but then B would be positive.


ah. It all makes sense now. I thought the "they both move on the same horizontal line" at the end of the question meant they were going in the same direction. Appears to not be.

thank you!
Original post by Rabadon
ah. It all makes sense now. I thought the "they both move on the same horizontal line" at the end of the question meant they were going in the same direction. Appears to not be.

thank you!


That's just telling you they are moving in the exact same direction, so you don't have to consider any components of the velocity. It also means the collision will be head on, and they both will continue to travel in the same direction after the collision.

No problem :smile:

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