How Do You Calculate Mechanical Energy and Work for a Thrown Ball?

[new^2^physics]

Please help... with Mechanical Energy Question

Homework Statement

A 0.50 kg rubber ball is thrown into the air. At a height of 20 m above the ground, it is traveling at 15 m/s.
a. what is the balls kinetic energy
b. What is its gravitational potential energy relative to the ground?
c. how much work was done by someone at ground level throwing the ball into the air?
d. What was the speed of the ball when it left the ground?

The Attempt at a Solution

a. Ek = 1/2 mv2
Ek = 1/2 (0.50kg)(15m/s)
Ek = 1/2 (0.50 kg)(225 m2/s2)
Ek = 1/2 (112.5 J)
Ek = 56 J

b. Eg = mgh
Eg = (0.50kg)(9.80 N/kg)(20m)
Eg = 98 J

c. W = fd
HELP ME PLEASE

 

[member 553083]

....d. Vf^2 = Vi^2 + 2ad Vf = 0m/s Vi = ? a = 9.8 m/s2 (acceleration due to gravity) d = 20m 0m/s = Vi2 + (2)(9.8 m/s2)(20m) Vi2 = -392 m2/s2 Vi = 19.8 m/s