Simply
T = 2 pi r/v
I = dq/dt = delta q/delta t here
is there any chnage in q for a quark? nope!
so,
i = q(quark) v/2 pi r (since we are interested in the period - that is the time change)
Let pi = (PI) and q = q of quark
I = QV/(2(PI)r)
the rest is very easy having in mind the...