\[(a)\;125 \;m \quad (b)\;200\; m \quad (c)\;100\; m \quad (d)\;80\; m\]

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The distance covered in first 3 second

$s=\large\frac{1}{2} $$gt^2$

$\quad=\large\frac{1}{2} $$ \times 10 \times 3^2$

$ \quad=45$

If the ball takes 'n' second to fall to ground . The distance covered in $n^{th}$ second

$s_n=u+\large\frac{g}{2}$$(2n-1)$

$\quad=0+\large\frac{10}{2}$$(2n-1)$

$\quad=10n-5$

Therefore $45=10n-5$

$n=5$

Therefore $ h=\large\frac{1}{2} $$gt^2$

$\qquad=\large\frac{1}{2} $$\times 10 \times 25$

$\qquad=125 \;m$

Hence a is the correct answer.

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