Question

13. A ball is thrown vertically upwards. It returns
6 later. Calculate : (i) the greatest height reached
by the ball, and (ii) the initial velocity of the ball
(Thke g = 10 m ) Ans. (i) 45 m. (ii) 30 m​

Answer 1

(i) 45 m, (ii) 30 m s−1

The ball is thrown up and it returns in 6sec, 

Time of accent = Time of decent

So, time to reach the highest point =6/2=3s

 By 2nd equation of motion

s=ut+21gt2

 To calculate height, consider motion of the ball from highest point to the ground

H=21gt2=21×10×32=45 m

 To calculate projection velocity, consider motion of the ball from projection to return to the point of projection.

0=ut−21gt2

u=10×6/2=30 m/s