physics
posted by Anonymous .
A boy reaches out of a window and tosses a ball straight up with a speed of 10 m/s. The ball is 20 m above the ground as he releases it. Use energy to find The ball's speed as it passes the window on its way down and speed of impact on the ground.

Kinetic energy on the way up = kinetic energy on the way down, ignoring airresistance.
Therefore speed going up = speed going down = 10 m/s.
Energy at window level = (1/2)mv0²+mgH
Energy at ground level = (1/2)mv²
Equate energies and solve for v. 
Calculated it comes out to be 22
Kinematics can also be used