A cricket ball is dropped from a height of 20 meters.
(a) Calculate the speed of the ball when it hits the ground.
(b) Calculate the time it takes to fall though this height `(g=10 m//s^(2))`

Explanation

Here ,Initial speed u=0
Final speed v=? (to be calculated )
Acceleration due to gravity `g=10m//s^(2)` (Ball comes down)
height h=20 m
Now we know that for a freely falling body
`v^(2)=u^(2)+2gh`
`v^(2)=(0)^(2)+xx10 xx20`
`v^(2)=400`
`v=sqrt(400)`
v=m//s
Thus the speed of cricket ball when it hits the ground will be 20 meters per second
(b ) Now , Intial speed u=0 n
Final speed v=20 m/s (calculated above )
Acceleration due to gravity `g=10 m//s^(2)` And Time,t =? (to be calculated )
Putting these values in the formula :
we v=u+gt
`20 =0+10 xx t`
10 t= 20 ltnrgt `t=20/10`
t= 2 s
Thus the ball takes 2 second to fall through a height of 20 metres .