A person sitting in ground floor of a building notices through window, of height 1.5 m , a ball drop

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2.Motion in Straight Line

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A person sitting in the ground floor of a building notices through the window, of height $1.5 \;m ,$ a ball dropped from the roof of the building crosses the window in $0.1 \;s$. What is the velocity (In $m/s$) of the ball when it is at the topmost point of the window $?\left( g =10\, m / s ^{2}\right)$

A

$20$

B

$15.5$

C

$14.5$

D

$4.5$

(NEET-2020)

Solution

From equation of motion

$S = ut +\frac{1}{2} at ^{2}$

$1.5= u (0.1)+\frac{1}{2} \times 10(0.1)^{2}$

$1.5=(0.1) u +0.05$

$u =15-0.5$

$\quad=14.5 m / s$

Standard 11

Physics

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