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\textbf{Math 220 (section AD?) \hfill Quiz 6 \hfill Fall 2014} \\
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\textbf{Name}\ \rule{4in}{0.4pt} \hfill
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$\bullet$ You have 15 minutes \hfill $\bullet$ No calculators \hfill $\bullet$ Show sufficient work
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\item (4 points) A man is standing on a bridge over a river. He reaches over the railing and throws a stone vertically upward. Until it lands in the river, the stone's height in feet above the river is $\D{h = -16t^2 + 8t + 24}$ where $t$ is measured in seconds since the stone was thrown.
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\item What is the maximum height reached by the stone?
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\item What is the velocity of the stone as it strikes the river?
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\item (3 points) There is a launch site of a hot-air balloon on the ground $90$ meters away from an observor. The balloon rises vertically at a constant rate of $3$ meters per second. How quickly is the angle of elevation of the balloon increasing $40$ seconds after the launch?
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\item (3 points) Suppose that $A$ represents the number of grams of a radioactive substance at time $t$ seconds. Given that $\D{\frac{dA}{dt} = -0.25A}$, how long does it take $12$ grams of this substance to be reduced to $7$ grams?
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