Question

A ball is projected horizontally from the top of the hill with a velocity of 30m/s .If it reaches the ground 5 sec later, calculate the height of the hills

Answer 1

Who cares about horizontal speed? It does not change during the fall.
It is a vertical falling problem.
h = Hi + Vi t - (9.81/2) t^2
0 = Hi + 0 t - 4.9 t^2
so
Hi = 4.9 t^2 = 4.9*25 or around125 meters

Answer 2

h = 1/2 gt^2