A 10 kg ball is dropped from a height of 10 m. Find (a) the initial potential energy of the ball, (b) the kinetic energy just before it reaches the ground, and (c) the speed just before it reaches the ground.
(a) The initial PE = mgh = 10. 9.8 . 10 = 980 J
(b) The KE just before touching the ground = the PE at the highest point = 980 J
(c) (1/2) m v2 = 980
=> (1/2) 10 v2 = 980
=> v2 = 980/5 =196
The speed just before it reaches the ground =v = 14 m/s