# Firing a boat

A boat is moving with a velocity $v$ directly away from a gun located on the bank of a river.The gun fires a shell with a speed $u$ at an angle$\theta$ with the horizontal.If the shell hits the boat ,then the distance of the boat from the gun at instant the shell is fired is given by $s=\frac{1}{g} \times {au\sin\theta( u \cos\theta - v)} .$ What is the value of $a$?

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