A ball is thrown upwards from top of a tower 40,m high with a velocity of 10,m/s , time when it stri

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2.Motion in Straight Line

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A ball is thrown upwards from the top of a tower $40\,m$ high with a velocity of $10\,m/s$ , find the time when it strikes the ground ........$sec$ : $(g = 10\,m/s^2)$

A

$8$

B

$1$

C

$4$

D

$6$

Solution

$-40=+10 t-\frac{1}{2}(10) t^{2}$

$-4=t-\frac{1}{2} t^{2}$

$t^{2}-2 t-8=0 \Rightarrow(t-4)(t+2)=0$

$\therefore t=4 s$

Standard 11

Physics

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