Special Relativity and pion

How fast must a pion be moving, on average, to travel 9.0 m before it decays? The average lifetime, at rest, is 2.60 ✕ 10-8 s. (Answer in terms of c)

I'm not exactly sure what equations I have to use but I believe it relates to time dilation.

I originally didn't realize it was a time dilation problem and calculated that the speed would be .8666c but since it relates to time dilation im not sure how to go about solving it.

collinsmark
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How fast must a pion be moving, on average, to travel 9.0 m before it decays? The average lifetime, at rest, is 2.60 ✕ 10-8 s. (Answer in terms of c)

I'm not exactly sure what equations I have to use but I believe it relates to time dilation.

I originally didn't realize it was a time dilation problem and calculated that the speed would be .8666c but since it relates to time dilation im not sure how to go about solving it.

If $\tau$ is the time it takes the pion to decay in it's own frame of reference ($\tau$ = 2.60 × 10-8 s), what is t, the amount of time it takes to decay in your stationary frame of reference?
(you can answer this intermediate result in terms of c and v; or in terms of $\gamma$, your pick for now ).