Question

An aero plane is flying horizontally at an altitude of 3000 ft directly over an observer. If it is flying witha speed of 300 ft/sec, the rate at which it is moving away from the observer when it is at 5000 ft away from the observer is _____

• A. 240 ft/sec
• B. 360 ft/sec
• C. 120 ft/sec
• D. 225 ft/sec

Answer 1

The correct option is A

240 ft/sec

$y^2=x^2+{3000}^{2}y\frac{dy}{dt}=x\frac{dx}{dt}\frac{dy}{dt}=\frac{4000}{5000}300=240ft/sec$