A spacecraft is powered through a solar sail, which reflects sunlight. The area of the sail is 1 km^2, oriented perpendicular to the direction to the Sun. The spacecraft is at 1 AU from the Sun. The sunlight falling on the sail has a power of 1380W/m^2.
(a) Calculate the momentum in this sunlight, and from this derive the pressure exerted on the solar sail by the sunlight;
(b) What is the maximum mass of the sail for which the force from light exceeds the gravitational force from the Sun?
For (a), which forumulae should be used here? I didn't find anything useful online and have no idea of a systematic textbook that I can read.
For a single photon, the momentum p=E/c which depend on frequency or wavelength. But here only enegry flux and surface area are given.
For (b), I presume I should equate the gravitational force and the light pressure to solve for the mass. Or do I have to consider the escape speed of the solar system?
PS: This question is at the level of first year uni physics.