Transforming Four-Momentum between Inertial Frames

[Twoism]

Homework Statement

A particle's four momentum in a given inertial frame is [E,Px,Py,Pz]=[5 J, 5 N*s, 0, 0]. What is its four-momtenum in an inertial frame that moves in the +x direction at a speed of .8 c relative to the first frame?

Homework Equations

N/a

The Attempt at a Solution

Isn't the four-momentum of the particle in the other frame just [5 J,5 Ns,0,0] since all components are independently conserved...? or am I making this problem too simple?
Thanks!

 

[phyzguy]

No, it's not the same in a different frame. Energy and momentum are conserved in a given inertial frame, but they transform among themselves when you change from one inertial frame to another. Look up the Lorentz Transformation.