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An aeroplane flying at a constant speed, parallel to the horizontal ground, \sqrt3 km above it, is observed at an elevation of 60^{\circ} from a point on the ground. If, after five seconds, its elevation from the same point, is 30^{\circ}, then the speed (in km/hr) of the aeroplane, is :

  • Option 1)

    1500

  • Option 2)

    1440

  • Option 3)

    750

  • Option 4)

    720

 

Answers (2)

best_answer

 

Angle of Elevation -

If an object is above the horizontal line from the eye, we have to raise our head to view the object.

- wherein

angle of elevation

 

 

\tan 60^{\circ}=\frac{\sqrt{3}}{x}=\sqrt{3}

\Rightarrow x=1

\tan 30^{\circ}=\frac{\sqrt{3}}{y}=\frac{1}{\sqrt{3}}

\Rightarrow y=3

AB=2kms\; \; \; \; also\; \; \; Time=5seconds

speed=\frac{distance}{time}=\frac{2000}{5}\times \frac{18}{5}km/hr=1440km/hr


Option 1)

1500

Option 2)

1440

Option 3)

750

Option 4)

720

Posted by

Himanshu

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