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k10k
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#1
Report Thread starter 14 years ago
#1
I am stuck on this question:

3 perfect elastic particles: A, B and C with masses 3 kg, 2kg and 1kg respectively lie at rest in a straight line on a smooth table with B between A and C. Particle A is projected directly towards B with speed 5m/s and after A has collided with B, B collides with C.


Find the speed of each particles after the second impact.


I have drawn a few equation out of this (4 in fact) but I have 5 unknowns :confused:
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cktlee1
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#2
Report 14 years ago
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For collusion between A and B

e = speech of separation / speed of approach
1 = (v2-v1) / 5 => v2-v1 = 5

conservation of momentum:
5x3 = 3v1 +2v2 => 3v1 +2v2 = 15

Solve simultaneously u get v1 = 1 and v2=6


Collusion between B and C, using v2 from above as initial speed of B (ie. become u2) :
e = (v3-v2) /6 => 6=v3-v2

Conservation of Momentum:
6x2 = 2v2 + v3 => 12 = 2v2 + v3

solve simultaneously:
v3 = 8 and v2=2


Speed after second impact:
A = 1, B = 2, C =8


Erm...lol, health warning, I am not good at M2
let someone check my working before trusting me ^^"
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k10k
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#3
Report Thread starter 14 years ago
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You are right.
I forgot that e would be 1 :P
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