flux density = magnetic field = 3 T

R(max) = 0.5m

we have,

R = mv/(qB)

v(max) = R(max)qB/m

KE(max) = (mv²)/2   (we can only find max KE with this data)

T(time period) = 2.pi.m/(qB)

period of half cell = pi.m/(qB)

just put values & get the ans...