Em'power'ed

Age 16 to 18 Challenge Level:

If $p$ and $q$ are primes and $p^rq^s= p^tq^u$what can you say about the powers?

 

If $p^{r/s}$ is an integer what can you say about $r$ and $s$?

 

All three terms must be the same powers of 2 and 3.