Ball are dropped from the roop fo towar at fived interval if tiem . At the moment when ` 9th` ball reaches the groun the nth ball is `(3//4)` the heith of the tower Wgat the vale of ` n ? G= 10 m//s^2`.

Explanation

Let (t) be the time interval between two successive balls while falling . When `9th ` ball reaches the ground, the Ist ball is just to be dropped, os the time taken by the 9th ball to reach the groun
` =(9 -1) t= 8 t` .
`:. S= 1/2 xx g xx g xx (8t)^2 = 1/2 10 xx 64t^2 = 320 t^2 ` ...(i)`
Time taken by nth ball to fall `= (n-1) t`
Distance travelled ` = s- 3 S/4`
:. ` S/4 = 1/2 xx [(n-1)^2 t]^2 = 5 (n-a)t`
or S= 20 (n-1)^2 t^2` ...(ii)
From (i) and (ii) ` 320 t^2 = 20 (n-1)^2t^2`
On solving, ` n=5`.