Given:
height = 20 m
acceleration = 10 ms
Formula:
For free falling body,
1. v = gt
2. s = 1/2 gt2
time taken to strike the ground
s = 1/2 gt2
20m = 1/2 × 10 ms-2 × t2
t2 = \(\frac{40 m}{10 ms^{-2}}\)= 4s2
∴ t = 2s
3. Velocity of the ball when it strikes ground v = gt
v = 10ms-2 × 2s
v = 20ms-1