Question

A ball is thrown upwards with a velocity of 20m/s from the top of abuilding.The height of the point from where the ball is thrown is 25m from the ground. i)How high will the ball rise? ii)How long will it be before the ball hits the ground? (g=10m/s2)

Answer 1

u=20 m/s
height above ground it will reach = u^2/2g = 20 m
so total height of the ball = 45 m at the top

time to reach the top = u/g = 2 sec.

time to reach ground = 2 sec + sqrt(2h/g) = 2 + sqrt(45*2/10) = 5 sec