Question

a ball is thrown vertically upwards with a velocity of 20 m/s from a top of a multi storey building. the height of the point from where the ball is thrown is 25 m from the ground. how high the ball will rise? how long will it be before the ball hits the ground.​

Answer 1

Here is ur answer:

a) At heighest poing velocity will be 0

so by formula v2 = u2 - 2gh (here - is because you are moving against gravity)

so h = 20*20/2*10 = 20 m

so ball will rise upto 25+20 m from the ground.

b) in second part we have to calculate the time of journey from top of 25 m high building to ground.

for this we should use

-h = ut - gt2/2 [in this case we are using upward direction as + ve and downward as - ve]

so -25 = 20t - 10t2/2

or 5t2 - 20t - 25 = 0

or t2- 4t - 5 = 0

or (t+1)(t-5) = 0

or t = 5 , -1

so t = 5 sec.

Hope it's help u

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