The current in a circuit is a function of time and is given by: $I=I_{peak}cos(2\pi f t)$.

If the value of the current at $t=0\, sec$ is $5\,A$, and first reaches the value of $0\,A$ at $t=10\,sec$, what is the value of the frequency, $f$, and what is the value of the *rms* current $I_{rms}$?