An aeroplane flying horizontally 1000m above the ground is observed at an angle of elevation 600 froma point on the ground.Aftera flight of 10secondsthe angle of elevation at a point of observation changes to 300 .Find the speed of the plane in m/s.

Let us observe the following figure.

Let A and B be the two positions of the aeroplane and let O be the point of observation. 

and AC = BD = 1000 m

From the right triangle OCA, we have

From the right triangle ODB, we have

We need to find the speed of the plane.

Thus the speed of the plane is 115.47 m /s

  • 25

tan 60=opp/adj

      root 3     =1000/adj

adj=1000/root3

            =1000*root3/3

           =1732/3

               =577

now tan 30 

roo3/2=1000/x

      x=2000/root3

          x=1154

then subtracting 1154-577

=577m in 10 seconds

 =the speed is 57.7ms 

hope this to be right 

and helps u

  • 6
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