Someone plans to float a small, totally absorbing sphere 0.500 m above an isotropic point source of light, so that the upward radiation force from the light matches the downward gravitational force on the sphere. The sphere's density is 19.0 g/cm3, and its radius is 2.00 mm.

(a) What power would be required of the light source?

(b) Even if such a source were made, why would the support of the sphere be unstable?