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# Mech 2 Impulse help? watch

1. A collision occurs between particles A and B which are moving in opposite directions in the same straight line. The impulse of each particle in the collision is 2 Ns.
a) Given that A has mass 0.4kg and initial velocity 3m/s, calculate the final velocity.
b) Given that the velocity of B changes by 2.5m/s, calculate the mass of B.
c) Deduce the maximum value for the initial speed of B.

I've got a and b, but don't understand c?
Thanks
2. (Original post by AvM4N)
A collision occurs between particles A and B which are moving in opposite directions in the same straight line. The impulse of each particle in the collision is 2 Ns.
a) Given that A has mass 0.4kg and initial velocity 3m/s, calculate the final velocity.
b) Given that the velocity of B changes by 2.5m/s, calculate the mass of B.
c) Deduce the maximum value for the initial speed of B.

I've got a and b, but don't understand c?
Thanks
Look at the wording of (b) ... it could do one of two things?
3. (Original post by Muttley79)
Look at the wording of (b) ... it could do one of two things?
ahh, it would just be + or - the final velocity- in this case +?
4. (Original post by Muttley79)
Look at the wording of (b) ... it could do one of two things?
Actually I've just read the question again and I'm still confused. Can you assume the mass is still 0.8kg and the speed changes by 2.5m/s from b to c?
If so, 2=0.8v-0.8(v+2.5) which just cancels out to 0=0??
5. (Original post by AvM4N)
Actually I've just read the question again and I'm still confused. Can you assume the mass is still 0.8kg and the speed changes by 2.5m/s from b to c?
If so, 2=0.8v-0.8(v+2.5) which just cancels out to 0=0??
Yes the mass can't change - I used the conservation of momentum.
6. (Original post by Muttley79)
Yes the mass can't change - I used the conservation of momentum.
When I use this, thinking u in terms of v, I get
1.2-0.8v-2= -0.8+0.8v which cancels to 0=1.6v
Still can't figure out why I'm doing me wrong?
7. (Original post by AvM4N)
When I use this, thinking u in terms of v, I get
1.2-0.8v-2= -0.8+0.8v which cancels to 0=1.6v
Still can't figure out why I'm doing me wrong?
Use both particles as there is a collision - be careful with direction of travel.
8. (Original post by Muttley79)
Use both particles as there is a collision - be careful with direction of travel.
How do you know which way B travels after the collision though?
9. (Original post by AvM4N)
How do you know which way B travels after the collision though?
The question says they are moving in opposite directions before the impact so that implies diection after impact.

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