Answer
a) bottom of the antenna is at a higher potential
b) $0.39mV $
Work Step by Step
(a) Since the antenna is vertical, we know that the vertical component of the magnetic field is not effective. The horizontal component is the effective component of the Earth's magnetic field. Thus, according to the right hand rule, the induced electric field is upward and the bottom of the antenna is initially at a higher potential.
(b) We know that
$\epsilon=Bvlcos\theta $
We plug in the known values to obtain:
$\epsilon=(5.9\times 10^{-5}T)(25m/s)(85cm)(\frac{1m}{100cm})cos72^{\circ}$
$\epsilon=0.39\times 10^{-3}V=0.39mV $
