# Relativistic collision and max energy

## Main Question or Discussion Point

a relaticistic particle collide with another rest particle. what is the maximum energy transmitted to the particle after collision?

## Answers and Replies

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I guess that would be momentum times the speed of light - since you would have to re-define your particles if rest mass were transferred.

Regards,

Bill

100%
thats what happens when a photon is Absorbed

100%
thats what happens when a photon is Absorbed
How does that relate to relativistic particles that are not photons?

Regards,

Bill

what is the maximum amount converted to heat or the maximum amount transferred to the other particle?

what is the maximum amount converted to heat or the maximum amount transferred to the other particle?
I think the OP was fairly clear with respect to that.

Regards,

Bill

well we just had a thread about the other so i thought i would ask. it seems rather trivial if he is asking how much is transferred.

what is the maximum amount converted to heat or the maximum amount transferred to the other particle?
to the other particle.

Meir Achuz
Science Advisor
Homework Helper
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There is a lot of algebra in solving this.
The max energy to the target is when the projectile goes straight back in the cm system.
First you have to find the cm momentum P and energy E of the target particle.
Then change its momentum direction to go forward and LT P and E back to the lab system.

yes.but I can't solve this problem by very much algebra. I don't reach any logic result.
please give me a mathematic result.

Meir Achuz
Science Advisor
Homework Helper
Gold Member
Conservation of energy and momentum for the incident particle m rebounding backwards with momentum p, which transmits the most energy (assuming the target mass M>m), gives the equation
$$E_L+M=\sqrt{p^2+m^2}+\sqrt{(p+p_L)^2+M^2}$$, where$$E_L$$ and
$$p_L$$ are the incident energy and momentum.
It is not easy to solve for p, but that is what one of us must do.

why cant we just imagine that there is a massless spring between the 2 particles then go to a frame where the particles are both moving at the same speed? I would think that the answer would be obvious. unless I am missing something.

Meir Achuz
Science Advisor
Homework Helper
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You are missing all the work involved.
The spring is irrelevant.
You seem to be describing my first suggestion to go to the cm system where the momenta (not the velocities) are equal in magnitude. Either method I proposed has some complicated algebra. But we all learned algebra in high school.