A ball is thrown vertically upwards. It goes to a height 20m and then returns to the ground. Taking acceleration due to gravity g to be 10m/s^2 , find:
(a) The initial velocity of the ball
(b) The final velocity of the ball on reaching the ground and
(c) The total time of journey of the ball.
Given: maximum height, s= 20m, g= 10m/s^2
(a)If ‘u’ is the initial velocity, velocity is zero at the highest point
We know that,
\begin{array}{l} v^{2}-u^{2}=2 g s \\ 0-u^{2}=2(10)(20) \\ u^{2}=-400 m / s \\ u=20 m / s \end{array}
Here, the negative sign indicates that the motion is against gravity.
(b) If v1 is the final velocity of the ball when it strikes the ground,
Velocity at the maximum height reached is zero which is equivalent to the initial velocity for the journey of the ball towards the ground.
Distance covered, s=20m;
We know from the equation of motion;
\begin{array}{l} v^{2}-u^{2}=2 g s \\ v^{2}-0=2(10)(20) m / s \\ v^{2}=400 m / s \text { or } v=20 m / s \end{array}
(c) Time for which the ball stays in air, t=2u/g
t=2 (20)/10
= 4s
Lido
Courses
Quick Links
Terms & Policies
Terms & Policies