How to Determine the Angle of a Particle in the Laboratory Frame of Reference?

[mck]

A particle of mass m moves in a center of mass frame of reference with a momentum p=2m. The center of mass moves with a speed v along the axis in the frame of reference of the laboratory. What's the angle of the particle in the frame of reference of the laboratory.

What i think I have to do is to calculate the speed of the particle in the laboratory frame of reference, than it is just a simple trigonometric calculation. But I don't really know how to do this.

 

[tiny-tim]

Hi mck!

A particle of mass m moves in a center of mass frame of reference with a momentum p=2m. The center of mass moves with a speed v along the axis in the frame of reference of the laboratory. What's the angle of the particle in the frame of reference of the laboratory.

What i think I have to do is to calculate the speed of the particle in the laboratory frame of reference …

uhh? that's v.

Hint: momentum is the x,y,z components of 4-momentum, which is a 4-vector which transforms exactly the same way as an (x y z t) 4-vector.

So split p into pcosθ and psinθ, and transform them separately.