Question

A stone is dropped from the top of a tower travels 25 m in the last second of it's motion of g=10ms^2 height of the tower is?

Answer 1

it means that it's velocity in last second was 25m/s
now v=25
u=0
a=10
${v}^{2} = {u}^{2} + 2as \\ {25}^{2} = 0 + 2 \times 10 \times s \\ s = 31.25m$

Answer 2

Snth=u+a/2(2n-1)
25=0+10/2(2n-1)
25=5(2n-1)
5=2n-1
6=2n
n=3
now,
final velocity= u+at
v=0+10*3
v=30
so,
the height of tower=v^2-u^2/2a
s=30*30-0/2*10
s=900/20
s=45