Question

. A ball is projected vertically upwards from ground with an initial speed of 20 ms–1. What is maximum height of the ball from ground? How long after projection the ball is at maximum height from ground

Answer 1

Given:-

•Initial velocity(u)=20m/s

To find:-

•Maximum height reached by the ball(h)

•Time taken to reach maximum height(t)

Solution:-

We know that:-

•Final velocity(v)=0

•Acceleration due to gravity(g)= -10m/s²(as it is working against gravity)

Actual value of g at the surface of earth is 9.8m/s²,but we took 10m/s² in this case for convenience.

By using the 3rd equation of motion,we get:-

=>v²-u²=2gh

=>0-(20)²=2(-10)h

=>-400= -20h

=>h= -400/-20

=>h= 20m

Now,by using 1st equation of motion,we get:-

=>v=u+at

=>0=20+(-10)t

=>-20= -10t

=>t= -20/-10

=>t=2s

Thus:-

•Maximum height attained by the by the ball is 20m

•Time taken is 2s