A perfectly reflecting mirror has an area of 1 cm² Light energy is allowed to fall on it for 1h at the rate of 10 Wcm^-2. The force that acts on the mirror is

6.7 × 10⁻⁸N

Let E = Energy falling on the surface per second = 10 J

Momentum of photons

$ p =\frac{h}{λ}=\frac{h}{(c_1v)}$

On reflection,

Change in momentum per second  $= 2p = \frac{2E}{c}$

We know that,

Change in momentum per second = force

$F=\frac{2E}{c}=\frac{2×10}{3×10^8}$

$= 6.7 × 10^{-8} $ N