A stone is dropped from a height of 20 m.
(i) How long will it take to reach the ground?
(ii) What will be its speed when it hits the ground? (g = 10 m/s2)
Height, s=20m
Initial velocity, u=0
Acceleration due to gravity, g=10m/s2
Final velocity, v=?
Time taken, t=?
(i) Using relation,
s = ut + gt2
20 = 0 * t + * 10 * t2
20 = 0 + 5t2
t2 = = 4
t = 2s
(ii) For a freely falling body:
v2 = u2 + 2gh
= (0)2 + 2 * (10) * (20)
= 400
v = 20m/s
Thus, the speed of the stone when it hits the ground is 20m/s.