Answers

2016-04-07T09:53:07+05:30
Initial velocity of the ball(u)  = 40 m/s
We know that ,
At highest point velocity(v) = 0 m/s

From equation of motion,
v² - u² = 2as
0 - 1600 = 2gh
-1600 = 2 × -10 × h
h = -1600/-20
h = 80 m

s = ut + 1/2at²
h = ut + 1/2(-g)t²
80 = 40t -5t²
5t² - 40t + 80 = 0
t² - 8t +16 = 0
t² - 4t - 4t +16 = 0
t( t - 4 ) - 4( t - 4 ) = 0
(t-4)(t-4) = 0
t = 4 sec
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