IF the toss was straight upward, then the kinetic energy it got from the toss is the gravitational potential energy it has at the top, where it stops rising and starts falling.
The conservation of energy says that energy in an isolated system remains constant, that it is not created nor destroyed but transforms from one form of energy to another. So when the ball is thrown into the air, it has kinetic energy (KE). As it goes into the air, that kinetic energy transforms into gravitational potential energy (GPE). The higher it gets, the more GPE it has and therefore the less KE it has. At the top, all of it is transformed into GPE and there is no KE. But total energy at any point after the ball is thrown until it lands it has the same energy throughout.
Knowing this, you can set the beginning KE equal to the final GPE. KE = GPE
because you multiply 780 by 4 because if it has a constant speed meaning it will not change speed then you multiply it by 4 because it says in 4 hours ( I hope this helped)
