Answer
$p_r = 1.0\times 10^7~Pa$
Work Step by Step
We can use Equation (33-35) to find the radiation pressure:
$p_r = \frac{2I}{c}$
$p_r = \frac{2P}{A~c}$
$p_r = \frac{(2)(1.5\times 10^9~W)}{(1.0\times 10^{-6}~m^2)(3.0\times 10^8~m/s)}$
$p_r = 1.0\times 10^7~Pa$
