Question

Radiation from the Sun reaching Earth (just outside the atmosphere) has an intensity of 1.38 kW/m2. (a) 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. (b) For comparison, calculate the force due to the Sun's gravitational attraction. Assume that the speed of light and Earth radius are 2.998 × 108 m/s and 6.37 thousand km respectively. (a) Number Units (b) Number Units

Answer 1

substitute the values we get,

(a) The force acting of the earth due to the sun is given by F-PrA where pr is the pressure due to the light of the sun, since the earth absorbs all the incident energy, the pressure is given by: substitute into the force: FIA assume that the earth behaves like a flat disk perpendicular to the Sun's rays, the area covered by the sun is A R2, where R is the radius of the earth, so:

$F=[1.38*10^{3}*\pi *(6.37*10^{6})^{2}]/3*10^{8}$

$F=5.8*10^{8}N$

(b) The gravitational force between the sun and the earth is given by: r2 where ME5.98 x 1024 kg is the mass of the earth, M 2.0 x 1030 kg is the mass of the sun, and r 1.5 x 1011 m is the distance bet ween them. substitute with the values to get: 667 x 10-1 N m2kg.98 10 g)(2.0 x 10 kg) (1.5 x 1011 m)2 3.55 x 1022 N