It has been proposed that a spaceship might be propelled in the solar system by radiation pressure, using a large sail made of foil. how large must the surface area of the sail be if the radiation force is to be equal in magnitude to the sun's gravitational attraction? assume that the mass of the ship + sail is 1500kg, that the sail is perfectly reflecting, and that the sail is oriented perpendicular to the sun's rays. see appendix c in your book for needed data.

As you are trying to move a heavy box of mass m, you realize that it is too heavy for you to lift by yourself. there is no one around to , so you attach an ideal pulley to the box and a massless rope to the ceiling, which you wrap around the pulley. you pull up on the rope to lift the box. use g for the magnitude of the acceleration due to gravity and neglect friction forces. once you have pulled hard enough to start the box moving upward, what is the magnitude f of the upward force you must apply to the rope to start raising the box with constant velocity? express the magnitude of the force in terms of m, the mass of the box.