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Home  >>  JEEMAIN and AIPMT  >>  Physics  >>  Class11  >>  Motion in a Straight Line
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A stone is dropped from a $25^{th}$ storey of a multistoreyed building. and it reaches the ground in $5\; sec$. How many storeys does it pass through in the 1st second ? ( g = 9.8m/s )

\[(a)\;2 \quad (b)\;1 \quad (c)\;5 \quad (d)\;3\]

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1 Answer

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Let $'h'$ be height of each storey of building using $ s=ut+\large\frac{1}{2}$$at^2$
$25h=0 \times 5 +\large\frac{1}{2}$$ \times 9.8 \times 5^2$
$\quad h=4.9m/s$
Distance covered in 1st second
$s_n=u+g\bigg(n-\large\frac{1}{2}$$\bigg)$
$\quad=0+9.8\bigg(1-\large\frac{1}{2}$$\bigg)$
          = 4.9
Therefore it covers 1 storey in 1st second
Hence b is the correct answer.

 

answered Jun 21, 2013 by meena.p
edited Jul 24, 2014 by thagee.vedartham
 

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