Calculating Dust Particle Size in Solar System Orbit - Electromagnetism Help

[andyfreesty1e]

urgent electromagnetism help

Homework Statement

Assume that dust particle in the solar system are spherical, black and have a density of 2000kg/m^3. Use the total luminosity of the sun to calculate the time average poynting vector of the radiation at a distance r from the Sun. Hence estimate what is the maximum size of a dust particle that can be help in orbit by gravity around the sun without being blown away by radiation pressure.

Homework Equations

The Attempt at a Solution

I have no idea about finding the poynting vector

For the second bit do i use P=F/A and F=GMm/R^2, and P(radiation)=S/c?

 

[HPRF]

If you use the luminosity equation I=P/A you don't need to work out the pointing vector. The P value from the previous equation will give you that.

For your own info P=[HxE] is the Poynting vector.