A camera weighing 21 N falls from a small drone hovering 31 m overhead and enters free fall. What is the gravitational potential energy change (in J) of the camera from the drone to the ground if you take the following reference points (a) the ground being zero gravitational potential energy? (b) The drone being zero gravitational energy? What is the gravitational potential energy of the camera (c) before it falls from the drone and (d) after the camera lands on the ground if the reference point of zero gravitational potential energy is taken to be a second person looking out of a building 30 m from the ground?