Given initial velocity of the stone, u=5 ms−1, acceleration, a=−10 ms−2 (negative as it is in vertically downward direction)
At highest point, final velocity, v=0
From third equation of motion, v2−u2=2as
02−52=2×−10×s
Therefore, height attained by the stone, s=−25−20=1.25 m
Also we know that final velocity, v = u + at
or, time, t=v−ua
t=0−5−10
=0.5 s