Relativity problem involving a muon

[pstir2]

Homework Statement

A muon is a subatomic particle with an average lifetime of 2.2 microseconds when stationary. In a burst of cosmic rays in the upper atmosphere, muons are observed to have a lifetime of 16 microseconds. What speed are they traveling at to achieve this?

Homework Equations

Time Dilation, Length Dilation, Mass Dilation, along with a few astrophysics formulas

The Attempt at a Solution

So I'm thinking this is relativity.
I used the time dilation formula:
t_v=t₀/Sqrt[1-(v²/c²)]

and worked out the velocity to be 2.972 x 10⁸ m/s

My maths is fine (it doesn't need checking but check it if you want to). What I really need to know is if this is the correct process?

 

[gneill]

Yes, that's the right formula to be using.