Question 1106910
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A skydiver jumps from an altitude of 4000 m. Her height above the ground in metres after t seconds is given by the function h = -5t + 4000. 
She free falls until she is 875 m above the ground, then pulls her chute. How many seconds is her free fall? 
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You &nbsp;<U>INCORRECTLY</U>&nbsp; presented your function.


The correct form is  h = -5t^2 + 4000,  &nbsp;&nbsp;&nbsp;&nbsp;when the unit of length/distance  &nbsp;<U>the"meter"</U>&nbsp; is used.


It is the &nbsp;&nbsp;<U>STANDARD &nbsp;FORM</U>&nbsp;&nbsp; for the height &nbsp;&nbsp;<U>at &nbsp;FREE &nbsp;FALL</U>.


<pre>
To answer the question, you need to solve the quadratic equation


-5*t^2 + 4000 = 875.


====>  5t^2 = 4000-875 = 3125  ====>  t^2 = {{{3125/5}}} = 625  ====>  t = {{{sqrt(625)}}} = 25.


<U>Answer</U>.  25 seconds.
</pre>


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Be aware !  The solution by &nbsp;@addingup &nbsp;is &nbsp;&nbsp;<U>I N C O R R E C T  &nbsp;!</U>.