A plane at an altitude of 12,000 feet finds the angle of depression for a building ahead of the plane to be 10.4 degrees. With the building still straight ahead, two minutes later the angle of depression is 25.6 degrees. Find of the plane relative to the ground in feet per minute.

Answer 1

draw a diagram. At first sighting, the distance d1 is

d1/12000 = tan 10.4°

The second distance d2 is

d2/12000 = tan 25.6°

Since speed is distance/time,

s = (d1-d2 ft)/(2 min)

That will be in ft/min.