Special relativity velocity tansforms

[Vuldoraq]

[SOLVED] Special relativity velocity tansforms

Homework Statement

A K^{0} meson at rest decays into a \pi^{+} meson and a \pi^{-} meson, each having a speed of 0.85c.

If the K0 meson is traveling at 0.9c when it
decays, what is the greatest speed that one of the \pi mesons can have?

What is the least speed?

Homework Equations

v_{x}=v_{x}^{'}+u/(1+u.v_{x}^{'}/c^{2})

The Attempt at a Solution

I am a bit stuck when it comes to putting what values where. I think that to find the maximum speed the pions will be in the same direction as the meson, and to find the minimum speeds the pions will be moving in the opposite direction to meson. However I don't really know what speed to put where or if I'm even barking up the right tree.

Please could someone help?

 

[Vuldoraq]

Ok, I've done some calculations please could someone tel me if they are right?

Letting v_{x}^{'}=0.85c and u=0.9c and applying the above formula
in its form gives,

v_{x}=0.99c as the maximum velocity.

Then,

Letting v_{x}^{'}=-0.85c u=0.9c and applying the above formula
in its form gives,

v_{x}=0.21c as the minimum velocity.

does this look reasonable?

 

[michalll]

right