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Perfectly elastic collision

by bearhug
Tags: collision, elastic, perfectly
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bearhug
#1
Oct9-06, 09:08 AM
P: 79
2 blocks are free to slide along the frictionless wooden track. The block of mass m1=5.00 kg is released from A, while the block of mass m2= 10.0 kg initially sits @bottom of ramp. The blocks collide @ position Bin a perfectly elastic collision. To what height does m1 rise after collision?

Originally I thought of using Ki + Ui = Kf + Uf where U=mgh
so 1/2m1vi^2 1/2m2vi^2 + (mgh)i = 1/2m1vf^2 1/2m2vf^2+ (mgh)f
However I'm having a hard time figuring this out because I don't know what the velocities of either block is after collision. I do know that the initial of block 2 is 0 m/s. Can someone help me set this problem up? Any help is appreciated.
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Doc Al
#2
Oct9-06, 09:12 AM
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What else is conserved in every collision?
bearhug
#3
Oct9-06, 11:52 AM
P: 79
In every collision... momentum

bearhug
#4
Oct9-06, 11:54 AM
P: 79
Perfectly elastic collision

In elastic collisios kinetic energy
Doc Al
#5
Oct9-06, 11:58 AM
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Quote Quote by bearhug
In every collision... momentum
Right. You have to use that fact to solve this problem. (You just used conservation of energy--but that's not enough.)
bearhug
#6
Oct9-06, 03:38 PM
P: 79
Does gravitational potential energy have anything to do with this problem?
bearhug
#7
Oct9-06, 05:53 PM
P: 79
OK so I set up the problem beginning with (m1v1 + m2v2)i = (m1v1 + m2v2)f . Should I start this problem with block 1 m=5.0 kg w/ initial velocity after collision or before. If it's before than initial would be 0 but other wise it wouldn't. Since the question asks for the height after collision I was wondering if this needs to be considered in terms of what's initial and what's final. Any feedback please.
Doc Al
#8
Oct10-06, 11:48 AM
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Assuming I understand the problem correctly, here's how to approach it. First figure out the speed of block 1 just before it collides with block 2. Then analyze the collision to determine the speed of block 1 just after the collision. (That involves conservation of momentum and energy.) Once you know the speed of block 1 after the collision, figure out how high it goes.


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