Visible light of 5000 Å with an energy flux of 30 W cm⁻² falls on a perfectly absorbing surface of 20 cm² at normal incidence. What is the total momentum delivered to the surface in one hour?

Correct option is B

Correct answer is B
Calculation:
 Energy flux = 30 W/cm2
. Area of the surface = 20 cm2
Total energy falling on the surface in 1 second = Energy flux × Area
⇒ Total energy = 30 × 20 = 600 W
Total energy delivered in 1 hour = 600 × 3600 J
⇒ E = 2.16 × 106 J
 Momentum delivered, p = E/c
⇒ p = (2.16 × 106) / (3 × 108)
⇒ p = 7.2 × 10-3 kg m s-1