posted by matthew .
(Airplane & Radar) An airplane is flying (horizontally) at the height of 6 km on a flight path that will take it
directly over a radar tracking station (on ground). If the distance D between the plane and the radar is
decreasing at a rate of 300 km/hr, find the speed of the plane when D remains 10 km.
x^2 + h^2 = D^2
solve for x when D = 10 and h = 6
x = 8 (3,4,5 triangle)
2 x dx/dt + 2 h dh/dt = 2 D dD/dt
but dh/dt = 0
2 (8)v + 0 = 2 (10) 300
v = 3000/8