Question

the angles of an elevation of an aeroplane from a point on the ground is 45 degree.After a seconds of flight,the angle changes to 30 degree.if the palne is flying at a constant height of 2500 m,find the speed of the plane

Answer 1

first we find how far plane goes during 1 second
2500/d=tan45=1
d=2500 (d is distance of plane when angle at a point is 45 )
=> 2500/(2500+x)=tan30
x=2500(root3-1) { x is distance covers by plane}
now speed=distance/time
=2500 (root3-1)/1 m/sec