Question 1130887
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&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;The solution by @josgarithmetic is &nbsp;&nbsp;<U>T O T A L L Y  &nbsp;&nbsp;W R O N G</U>&nbsp;&nbsp; and does not follow the problem condition.


&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;So I came to bring a correct solution, &nbsp;which is below.



<pre>
F, force
A, area
v, velocity
k, variation constant



F = {{{kAv^2}}}

k = {{{F/Av^2}}}

k = {{{50/(500*40^2)}}}

k = {{{1/(10*40^2)}}}

k = {{{1/16000}}}

-

F = {{{(1/16000)(Av^2))}}} = {{{(1/16000)*(2*80^2)}}} = 0.8 N.     <U>ANSWER</U>
</pre>

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By the way, are you familiar with the conception commonly accepted between educated and civilized people to thank after getting help ?