A broken spaceship is located 10 km above the center of a large circular thin sheet of unknown dust. The sheet has a radius of 10^6km and a density of 7x10^11kg/m^2. The spaceship and the dust attract each other due to the gravitational force. a) Discover the initial acceleration of the spaceship. b) Discover the acceleration of the spaceship right before the spaceship hits the dust. c) What will the astronauts in the spaceship experience right before the spaceship hits the dust?