**Given:**

Area of the mirror = 1 cm^{2} ,

Power transmitted to the mirror = 10 Wcm^{-2} ,

**Calculations: - **

The average force is given by \(\frac{Δp}{Δt}\)

Since the surface is perfectly reflecting we can write Δp = 2\(\frac{Δt}{c}\)

So F = 2 \((\frac{ΔE}{cΔt})\) = 2 \(\frac{p}c\)

=2 \(\frac{10\times10^4\times1\times10^{-4}}{3\times10^8}\)

= \(\frac{20}{3}\)x 10^{-8} N

= 6.7 x 10^{-8} N