It has been proposed to propel spacecraft through the Solar System with a large sail that is struck by photons from the Sun. (a) Which would be more effective, a black sail that absorbs photons or a...

It has been proposed to propel spacecraft through the Solar System with a large sail that is struck by photons from the Sun.

(a) Which would be more effective, a black sail that absorbs photons or a shiny sail that reflects photons back toward

the Sun? Explain briefly.

(b) Suppose that N photons hit a shiny sail per second, perpendicular to the sail. Each photon has energy E. What is the

force on the sail? Explain briefly.