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# m1 Direction of impulse watch

1. hi, for part b in this question I get a positive value and a negative value for impulse. Can anyone explain what is wrong because the answer is the +v e value Attachment 501917501919 impulse for both particles are both going to the left. I don't get what I did is wrong.. thanks
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2. (Original post by coconut64)
hi, for part b in this question I get a positive value and a negative value for impulse. Can anyone explain what is wrong because the answer is the +v e value Attachment 501917501919 impulse for both particles are both going to the left. I don't get what I did is wrong.. thanks
The string is giving particle P an impulse to the right since the tension in the string will force the particle to the right.

So if you're finding the change of momentum of P then you should take right as positive.

The impulse of P on the string (equivalent to the impulse on P) is to the left but you're not finding the change in momentum of the string.
3. (Original post by notnek)
The string is giving particle P an impulse to the right since the tension in the string will force the particle to the right.

So if you're finding the change of momentum of P then you should take right as positive.

The impulse of P on the string (equivalent to the impulse on P) is to the left but you're not finding the change in momentum of the string.
But overall p is moving to the left though and that's because the the push to the left... I can't really picture the impulse as acting to the right because p is projecting away from the other particle. Thanks
4. (Original post by coconut64)
But overall p is moving to the left though and that's because the the push to the left... I can't really picture the impulse as acting to the right because p is projecting away from the other particle. Thanks
Imagine you are facing left and your friend is facing right. You are connected to your friend by a rope which is attached to your backs.

Both of you run forward. Eventually the rope will jerk tight and pull you back towards your friend (to the right).

There is an impulse acting on you by the rope similar to your question.
5. (Original post by notnek)
Imagine you are facing left and your friend is facing right. You are connected to your friend by a rope which is attached to your backs.

Both of you run forward. Eventually the rope will jerk tight and pull you back towards your friend (to the right).

There is an impulse acting on you by the rope similar to your question.
But my friend would not be running though (modelled as a particle) so i wouldnt be pulled back...
6. (Original post by coconut64)
But my friend would not be running though (modelled as a particle) so i wouldnt be pulled back...
You're right - I didn't check that part of the question.

But the reasoning still holds : your friend is stationary and you are running away from them. When the rope goes tight, you will experience a force in the opposite direction to your motion.
7. (Original post by notnek)
You're right - I didn't check that part of the question.

But the reasoning still holds : your friend is stationary and you are running away from them. When the rope goes tight, you will experience a force in the opposite direction to your motion.
Oh okay then, I guess it does make sense in a way. Thank you

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