A bird is sitting on the top of a vertical pole 20   m high and its elevation from a point O on the…

A bird is sitting on the top of a vertical pole 20 m high and its elevation from a point O on the ground is 45°. It flies off horizontally straight away from the point O. After one second, the elevation of the bird from O is reduced to 30°. Then the speed (in m/s) of the bird is 
  1. 2 0 2
  2. 2 0 3 - 1
  3. 4 0 2 - 1
  4. 4 0 3 - 2

Solution

​

   AD=20 m

   AO=20tan45∘=201=20 m

   CB=20 m

∴BO=20tan30∘=2013=203m

∴  AB=BO-AO

= 2 0 3 - 2 0

=203-1m

It took 1 sec to travel distance DC.

∴ Speed =203-1 m/sec.

Asked in: JEE Main 2014 (06 Apr)

Practice more Heights and Distances questions on Aicharya