How Do You Find the Total Energy and Speed of a Relativistic Particle?

[kikko]

Homework Statement

Mass of particle = 5GeV/C^2
Momentum of particle = 5GeV/c

Find total energy of particle and speed of particle.

Homework Equations

E=λmc^2
p=λmu
λ=(√(1-(u/c)^2))^-1

The Attempt at a Solution

When I try so solve for speed, I realize λ is a function of u, so get this:

(u*(√(1-(u/c)^2))^-1) = p/m = c, but can't solve for u from that.

How would I go about approaching this problem?

 

[vela]

Try finding another relationship between E, p, and m in your textbook.

You can solve for u in your approach, but your assertion that p/m=c isn't correct.