What power (in Watts) must the beam of a 0.5 kg flashlight deliver
if the recoil momentum of the outgoing photons is to suspend the
flashlight against the earth's gravity? (Assume that all photons from
the bulk are visible photons with wavelength 
Å.)
A certain flashlight bulb consumes 10 Watts of electrical power. If
the conversion efficiency from electrical power to light energy is
, what mass could the outgoing beam of light be able to
suspend against the earth's gravity? By what percentage is this
force, when averaged over a period of one second, expected to
fluctuate?