Question

A basketball is tossed up at an initial speed of 20 m/s.

Answer 1

Gravity slows the upward speed of any rising object by 9.8 m/s every second.

If the ball is tossed upward at 20 m/s, then it's at the top of its arc and its speed has dwindled to zero in (20/9.8) = 2.04 seconds.

During that time, its starting speed is 20 m/s and its ending speed is zero, so its AVERAGE speed all the way up is (1/2) (20 + 0)  =  10 m/s .

Sailing upward for 2.04 seconds at an average speed of 10 m/s, the ball rises to (2.04 x 10)  =  20.4 meters.