Answer
$T = 3.66~s$
Work Step by Step
Note that $v = \frac{2\pi~r}{T}$
At the bottom of the track:
$\sum F = \frac{mv^2}{r}$
$F_N-mg = \frac{m(2\pi~r)^2}{T^2r}$
$2.50~mg-mg = \frac{m(4\pi^2~r)}{T^2}$
$1.50~g = \frac{4\pi^2~r}{T^2}$
$T^2 = \frac{4\pi^2~r}{1.50~g}$
$T = 2\pi~\sqrt{\frac{5.00~m}{(1.50)(9.80~m/s^2)}}$
$T = 3.66~s$