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A ball is thrown vertically upward with a velocity

A ball is thrown vertically upward with a velocity of 20 ms-1 from a top of a multistory  building.The hight of the  point from where  the ball is thrown is 25 m from the ground. The hight to which the ball rises from the ground and time taken before the ball hits the ground are (g:=10 ms-2)

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 V^{2}= u^{2}+2as\Rightarrow O=2o^{2}+2\times \left ( -10 \right ).H_{max}

H_{max}= 20m

Maxmium height from the ground :20 + 25 = 45m

Time to reach ground

S=-25m, u=20 ms-1, a =-10 m/s2

\Rightarrow S=ut +\frac{1}{2}at^{2}\Rightarrow -25m= 20 t-5t^{2}\\* or t= -1\: or 5 sec\\*\therefore t= 5\: sec

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