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{\bf Question}

A stone is dropped from a balloon rising at 10ms$^{-1}$ and
reaches the ground in 8 seconds.  How high was the balloon above
the ground when the stone was dropped.

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{\bf Answer}

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Newton's 2nd law:  $m\ddot{y} = -mg \Rightarrow  \ddot y = -g$

Initially the stone has speed 10ms$^{-1}$ \underline{upwards}.

Therefore $ y = 10 t - \frac{1}{2}gt^2 + H$

$y = 0$ at $t = 8 \Rightarrow H = 233$m.


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