Question

A 0.50 kilogram ball is held at a height of 20 meters. What is the kinetic energy of the ball when it reaches halfway after being released?

Answer 1

While the ball is held 20 meters above the floor,

                                   Potential energy = (mass) (gravity) x (height) =

                                                        (0.5 kg) x (9.8 m/s²) x (20 m) =  98 joules.

When it's dropped and reaches 1/2 of its initial height, it has half as much
potential energy.  The rest has turned into kinetic energy  =  49 joules.

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Want to know what else you can figure out ?  Watch this . . . 

                                                 Kinetic energy = (1/2) x (mass) x (speed)²

                                                          49 joules = (1/2) x (0.5 kg) x (speed)²

Divide each side by (0.25 kg):       49 joules / 0.25 kg = speed²

Take the square root of each side:        7/0.5 = speed = 14 meters per second

That's the speed of the ball after falling 10 meters ! 
How cool is that !