Completely Elastic Proton Collision

AI Thread Summary
The discussion revolves around solving a completely elastic collision problem involving two protons, where one proton is initially at rest. Key points include the setup of momentum equations in both the x and y directions, with the challenge of having three unknowns and only two equations. Participants suggest using conservation of energy to create a third equation, which would allow for solving the system. The conversation emphasizes that Coulomb repulsion can be ignored for this problem, likening the protons to billiard balls. Ultimately, the focus is on applying conservation principles to find the post-collision velocities and angles.
akatz
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[SOLVED] Completely Elastic Proton Collision

In my physics class we tried to solve this problem but nobody in the class could figure it out and the teacher was having difficulty with it. It is possible that the book put in a problem that isn't possible to solve...

i am not very good with latex coding so feel free to ask about my sub/superscript system

A proton (atomic mass 1.01 u) with a speed of 518 m/s collides elastically with another proton at rest. The original proton is scattered 64.0 degrees from its initial direction.
(A) What is the direction of the velocity of the target proton after the collision?
(B) What are the speeds of the two protons after the collision?

Homework Statement



A proton (atomic mass 1.01 u) with a speed of 518 m/s collides elastically with another proton at rest. The original proton is scattered 64.0 degrees from its initial direction.

Variables
m_{1}=1.01 u
v_{1}=518 m/s
m_{2}=1.01 u
v_{2}=0 m/s
v^{'}_{1}=?
v^{'}_{2}=?
\vartheta=64 degrees (b/n path of first proton before and after collision)
\varphi=? (b/n path of second proton after collision and path of first proton before collision)

Homework Equations



Total momentum before equals total momentum after
P_{T}=P^{'}_{T}
momentum = mass X velocity
P=mv

The Attempt at a Solution



we set up a force diagram so that the path of proton #1 is a horizontal line
vvvv total momentum in X direction vvvv
P_{T,X}= 518 u\timesm/s=V^{'}_{1}cos(64)+V^{'}_{2}cos(\varphi)
we have three variables in this equation and this makes a problem to solve for just one variable

Total momentum in Y direction is zero prior to collision and therefore is zero after collision
P_{T,Y}=0 u\timesm/s=V^{'}_{1}sin(64)+V^{'}_{2}sin(\varphi)

this is the point where I have absolutely no idea what to do and apparently my teacher and the rest of the class as well...
Any help/hint(s) would be very greatly appreciated
Thanks,
Akatz
 
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Are we supposed to ignore the Coulumb repulsion? Could we replace the protons with billiard balls of the same mass?
 
yes you can ignore couloumbs law
good idea...think of the protons as two billiard balls
 
Ok, so right now you have 2 equations with 3 unknowns. You need one more equation in order to solve this problem. Try using conservation of energy (only accounting for kinetic energy). You'll end up with an equation for each p(x-direction), p(y-direction), and energy with unknowns, v1, v2 and the angle the 2nd ball makes with the original trajectory. Does this help?
 
thats what i did
i have the equation for conservation of momentum in the y axis
and i have conservation of momentum in the x axis
and that is where i am stuck
thanks for the help
i could isolate the unknown i am trying to find but it would be defined in terms of other unknowns
guh...
 
Use conservation of energy. Only kinetic energy terms will appear. This will give you 3 equations with 3 unknowns. Have you seen conservation of energy before?
 
yes
ok i think i get what your saying now
Thanks a ton!
 
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