When an object is moving along a straight line with constant acceleration, the object is said to be

Question

When an object is moving along a straight line with constant acceleration, the object is said to be in uniformly accelerated motion. For example, when a man is standing on the top of a building of height 40 m and he throws a ball up in the air, ball travels in straight line. The ball reaches to a maximum height in 2 s and then it falls down to the building due to effect of gravity.\ The velocity of ball just before reaching maximum height (in $\mathrm{m} / \mathrm{s}$ ) is

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(b) : Using equation of motion, $v^2-u^2=2 g s$ $ \  \begin{aligned} & v^2-0=2 	imes 10 	imes 40 \ & v^2=800 \Rightarrow v=28.3 \mathrm{~m} / \mathrm{s} \end{aligned} $