Answer
$F = 1.66\times 10^{-11}~N$
Work Step by Step
In part (b), we found that the radiation pressure is $p_r = 13.2~Pa$
We can find the force on the sphere:
$F = p_r~A$
$F = p_r~\pi~r^2$
$F = (13.2~Pa)~(\pi)~(633\times 10^{-9}~m)^2$
$F = 1.66\times 10^{-11}~N$
