Question

a ball is thrown vertically upward. it goes to a height of 19.6 and then returns back to the ground. find the
1. initial velocity of the the ball
2. total time of journey
3. final velocity of the ball when it strike the ball

Answer 1

let initial velocity be u
and at the maximum height I.e; s=19.6m
velocity will be zero
so let's consider first the journey of ball from ground to height 19.6m
we have ,
s=19.6m
v=0m/s
g=(-9.8m/s²)
u=???
t(time taken by the ball to reach that height)=????
so using formula,
v²=u²+2as
=>(0)²=u²+2(-9.8)(19.6)
=>u²= (2×2)×(9.8×9.8)
=>u=2×9.8
=>(i.)u=19.6m/s this is the initial velocity of the ball
now for t,
(v-u)/t=a
(0-19.6)/t=(-9.8)
t=2seconds
so the same time will be taken by the ball to reach the ground from this height
therefore, (ii.) total time of the journey is 4seconds
and it will hit the ground with the same velocity with which it was thrown
therefore,(iii.) final velocity of the ball=19.6m/s