Answer
(a) $P = m~g~c$
(b) $P = 73.5~W$
Work Step by Step
(a) The required force is $F = mg$
We can find the required power $P$:
$F = \frac{P}{c}$
$P = F~c$
$P = m~g~c$
(b) We can evaluate our expression for $P$:
$P = m~g~c$
$P = (25\times 10^{-9}~kg)(9.8~m/s^2)(3.0\times 10^8~m/s)$
$P = 73.5~W$
