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M2 Collisions watch

1. Hey, so heres the question I'm stuck on (part b)

A particle P of mass 3m is moving with speed 2u in a straight line on a smooth horizontal plane. The particle P collides directly with a particle Q of mass 4m moving on the plane with speed u in the opposite direction to p. The coefficient of restitution between p and Q is e

a.) Find the speed of Q immediately after the collision

I calculated this to be Vq=(1/7)(2+9e)u

Given that the direction of motion of P is reversed by the collision,

b) find the range of possible values of e

I need some help on this one. Thanks TSR
2. (Original post by xyz9856)
Hey, so heres the question I'm stuck on (part b)

A particle P of mass 3m is moving with speed 2u in a straight line on a smooth horizontal plane. The particle P collides directly with a particle Q of mass 4m moving on the plane with speed u in the opposite direction to p. The coefficient of restitution between p and Q is e

a.) Find the speed of Q immediately after the collision

I calculated this to be Vq=(1/7)(2+9e)u

Given that the direction of motion of P is reversed by the collision,

b) find the range of possible values of e

I need some help on this one. Thanks TSR
What's the velocity of P after the collision? (In terms of e) If it reverses direction shou that velocity be > 0 or < 0?
3. (Original post by Zacken)
What's the velocity of P after the collision? (In terms of e) If it reverses direction shou that velocity be > 0 or < 0?
since i set P as positive before it should be <0 after collision?
4. (Original post by xyz9856)
since i set P as positive before it should be <0 after collision?
Yeah, so find in terms of , then set and solve for . For example, if I found that then I can say that (this is just an example, your will be something different that you need to work out for yourself, do you know how to?)- remember to make sure that . Clear?
5. (Original post by Zacken)
Yeah, so find in terms of , then set and solve for . For example, if I found that then I can say that (this is just an example, your will be something different that you need to work out for yourself, do you know how to?)- remember to make sure that . Clear?
finally, that took me quite some time to get my head around. 1/6<e<1 was my answer. Im finding M2 and M1 quite tricky. How do I get myself to 100UMS standard between now and the exams (I believe they are in June, 8th and 17th). Thank you.
6. (Original post by xyz9856)
finally, that took me quite some time to get my head around. 1/6<e<1 was my answer. Im finding M2 and M1 quite tricky.
First class work.

How do I get myself to 100UMS standard between now and the exams (I believe they are in June, 8th and 17th). Thank you.
Practice.
7. (Original post by Zacken)
First class work.

Practice.

thanks Zacken, good luck with your exams also. I hope to be in a similar place to you at this time next year, except with engineering
8. (Original post by xyz9856)
thanks Zacken, good luck with your exams also. I hope to be in a similar place to you at this time next year, except with engineering
No problem - glad I helped. Good luck with your exams as well! TSR is here for any more questions you have.
That's very kind of you to say.
9. (Original post by xyz9856)
since i set P as positive before it should be <0 after collision?
How do you know if p is <0 or >0 after the collision?
10. (Original post by mohamed-essa)
How do you know if p is <0 or >0 after the collision?
Depends on whether you said p>0 before the collision. If you said p > 0 before then it's p < 0 after. If you said p < 0 before than it's p > 0 after.
11. (Original post by Zacken)
Depends on whether you said p>0 before the collision. If you said p > 0 before then it's p < 0 after. If you said p < 0 before than it's p > 0 after.
Thanks man.
12. (Original post by mohamed-essa)
Thanks man.
You're welcome!

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