Answer :
Answer: The distance between the man and the plane increasing at a rate of 400ft/s
Explanation: Please see the attachments below



The rate of distance will be "300 ft/s".
Let,
- The horizontal distance between the man and the base will be "x".
- The distance between man and plane will be "D".
We know,
The rate,
- 500 ft/s
then,
- [tex]\frac{dx}{dt} = 500[/tex]...(1)
By using Pythagoras theorem, we get
→ [tex]x^2+3000^2 = D^2[/tex]
[tex]D = \sqrt{x^2+3000^2}[/tex]
Differentiating both sides with respect to time, we get
→ [tex]\frac{dD}{dt} = \frac{x}{\sqrt{x^2+3000^2} }\times \frac{dx}{dt}[/tex]
By substituting the "x=4000" and using (1), we get
→ [tex]\frac{dD}{dt} = \frac{4000}{\sqrt{4000^2+3000^2} }\times 500[/tex]
[tex]= \frac{3000}{1000\sqrt{16+9} }\times 500[/tex]
[tex]=\frac{1500}{5}[/tex]
[tex]= 300 \ ft/s[/tex]
Thus the above approach is correct.
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