Question

Assuming that Earth (and its atmosphere) behaves like a flat disk perpendicular to the Sun's rays and that all the incident energy is absorbed, calculate the force on Earth due to radiation pressure. What would it be for Pluto? What is the force on the Earth due to the sun's gravitational attraction? What is it for Pluto?

Answer 1

here the sun reaching earth has an intensity 1400 w/m^2

1. Intensity at Pluto = 1400/(39.48^2) = 0.900 W/m^2[Distance of Pluto from Sun 39.48 AU]
2. Radiation pressure = I/c =1400/(3*10^8)
Force on earth = [pi*(6.0*10^6)^2*1400]/(3*10^8) N = 5.28*10^8 N
3. Force on Pluto = (5.28*10^8)*(0.900/14000)*(1.180/6.0)^2 = 1.31*10^4 N
4. Gravitational force on Earth = [(6.67*10^-11)*(1.989*10^30)*(6.0*10^24)...
= 3.58*10^26 N
5. Gravitational force on Pluto = (3.58*10^26)/[(39.48^2)*(600/1.3)] = 4.97*10^20 N
{mass of Pluto = 1.3*10^22 kg)