Question 318868
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First convert 45 miles per hour to feet per second.  The first step to that conversion is to do a quick calculation in your head so that you will know that the calculated answer is reasonable.  Half of 45 rounded down is 22, 22 plus 45 is 67 -- so 67 feet per second is a good estimate of 45 miles per hour.  Now do it with the calculator.


*[tex \LARGE \ \ \ \ \ \ \ \ \ \ 45\ \text{mph}\ \times\ \frac{5280}{3600}\ =\ 66\ \text{fps}]


Comparing that result to the "in the head estimate" tells us we are on the right track.



Now all you need to do is divide 420 feet by 66 feet per second.  I'll leave that arithmetic up to you.



John
*[tex \LARGE e^{i\pi} + 1 = 0]
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