Kyoko is standing at the base of a hill holding a balloon filled with helium. She releases the balloon and it starts to float upwards. From which direction will Hiroshi, who is standing on top of the hill, see the balloon rise?
Respond very briefly.
Hiroshi, standing on top of the hill, will see the balloon rise from below his horizontal plane of view and continue to rise upwards. The balloon filled with helium rises because it is less dense than the surrounding air. Since Kyoko is at the base of the hill and Hiroshi is at an elevated position, the balloon's ascent would begin at a lower altitude relative to Hiroshi's position. As the balloon ascends, it will continue to move away from the ground where Kyoko is, and closer to Hiroshi's eye level, eventually passing it if it ascends high enough.