If a $20-$kg object dropped in air has a terminal speed of $60\frac{m}{s},$ what was its acceleration at $30\frac{m}{s}?$

$9\mathrm{.}80\frac{m}{s^2}$

$7\mathrm{.}35\frac{m}{s^2}$

$4\mathrm{.}90\frac{m}{s^2}$

$2\mathrm{.}45\frac{m}{s^2}$

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