Momentum conservation - particle collision

AI Thread Summary
Momentum conservation in particle collisions is addressed by recognizing that total momentum is conserved in both horizontal and vertical directions. In this scenario, two alpha particles, each with a mass of four protons, move in opposite horizontal directions, which allows their momenta to cancel out, thus conserving horizontal momentum. The vertical momentum is also considered, as the two alpha particles must have equal and opposite vertical momentum to balance the initial momentum of the proton directed at a stationary lithium target. The confusion arises from the assumption that the total momentum after the collision is zero; however, it is essential to account for the initial momentum of the proton, which influences the final state of the system. Overall, the conservation of momentum holds true as long as all components of momentum are considered.
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Homework Statement



http://s359.photobucket.com/albums/oo40/jsmith613/?action=view&current=MomentumConservation.png

MomentumConservation.png

Homework Equations


The Attempt at a Solution



Working out how momentum is consered in this situation,...

I know that the mass of an alpha particle is 4*mass of proton...however, I am still slighly concerned because the alpha particles move in opposite vertical directions hence their momenta cancel...how is momentum conserved here (I know that horizontal momentum is conserved but how is vertical momentum conserved)??
 
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From the picture, the alpha particles don't seem to quite move in opposite directions. In any case, the horizontal momentum is absorbed by the foil, and ultimately by what's holding the foil in place.
 
vela said:
From the picture, the alpha particles don't seem to quite move in opposite directions. In any case, the horizontal momentum is absorbed by the foil, and ultimately by what's holding the foil in place.

but you cannot deny both alpha particles have horizontal momenta (but they must cancel to conserve linear momentum)...I guess that if the examiners were to ask a question about this in my exam they would make the diagram clearer...or they would simply ask me what I knew about the momenta of the particles.

Would the following answer be correct:

"As no external forces act the total momentum is conserved. Therefore the two alpha particles must move in opposite horizontal directions to conserve horizontal momentum. The total vertical momentum of both alpha particles must be equal in magnitude AND direction to the momentum of the proton"
 
I have drawn a blue line to show that the vertical momentum are in differnt directions...
 

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on reading about
"A proton is directed at a stationairy lithium target. The law of conservation of momentum states that the two alpha particles must have equal and opposite momentum"

How does this conserve momentum? If they are equal and opposite, it implies total momentum after is zero BUT total momentum before is not zero...what is going on?
 

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