Chapter 34 - Electromagnetic Fields and Waves - Exercises and Problems - Page 1031: 55

$I = 4.9\times 10^7~W/m^2$

The required force is $F = mg$ We can find the required power $P$: $F = \frac{P}{c}$ $P = F~c$ $P = m~g~c$ $P = (1.0\times 10^{-3}~kg)(9.8~m/s^2)(3.0\times 10^8~m/s)$ $P = 2.94\times 10^6~W$ We can find the required intensity: $I = \frac{P}{A}$ $I = \frac{2.94\times 10^6~W}{(8.5~in)(0.0254~m/in)(11~in)(0.0254~m/in)}$ $I = 4.9\times 10^7~W/m^2$