A 330 kg piano slides down a 37 degree frictionless incline and is kept from accelerating by a man who is pushing back on it parallel to the incline. Calculate (a) the force exerted by the man. (b) the work done by the man on the piano. (c) the work done by the force of gravity. And (d) the net work done on the piano. (Please show your work)

Amichelson interferometer operating at a 600 nm wavelength has a 3.02-cm-long glass cell in one arm. to begin, the air is pumped out of the cell and mirror m2 is adjusted to produce a bright spot at the center of the interference pattern. then a valve is opened and air is slowly admitted into the cell. the index of refraction of air at 1.00 atm pressure is 1.00028.how many bright-dark-bright fringe shifts are observed as the cell fills with air?