A stone is dropped from the tower covers a distance “7 S” in last second where S is distance covered in first second. How much time does the stone take to reach ground? (g=10m/s 2 )

For freely falling U=0,a=+g let n ' is last secdistance covered in nth second Sn=U+an−12 Then distance in first sec⁡S1=g1−12⇒S=g2---(1) Then distance in last sec⁡S2=gn−12⇒7S=g2n−12---(2)substitute equation (1) in (2)7g2=g2(2n−1)⇒2n−1=7⇒n=4 Hence the time of fall is 4 sec