Question

A kite is 100 ft. high and there are 260 ft. of cord out. If the kite is moving horizontally at rate of $6\frac{1}{2}$ miles per hour directly away from the person who is flying it; how fast is the cord being paid out ?

• A. $\frac{6}{5}$ miles/hour
• B. 6 miles/hour
• C. $6\frac{1}{2}$ miles/hour
• D. 3 miles/hour

Answer 1

Answer: (B)

6 miles/hour

Answer 2

x² + h² = y²

$x\frac{dx}{dt} = y\frac{dy}{dt}$

$\frac{dy}{dt} = \frac{\frac{13}{2}\sqrt{(260)^{2} - (100)^{2}}}{260}$ = $\frac{13.4.60}{2.260} = 6m/h.$