# 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 )

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

## 1 Answer

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
edited Jul 24, 2014

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1 answer

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1 answer