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A man on the top of a vertical tower observes a car moving at a uniform speed
towards the tower on a horizontal road. If it takes 18 min. for the angle of
depression of the car to change from 30 \degree to 45 \degree
; then after this, the time taken
(in min.) by the car to reach the foot of the
tower, is :

  • Option 1)

    9(1+\sqrt3)

  • Option 2)

    18(1+\sqrt3)

  • Option 3)

    18(\sqrt3-1)

  • Option 4)

    9/2(\sqrt3-1)

 

Answers (2)

best_answer

As we have learned

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 45\degree= h/x

\tan 30\degree= h/x+18

\sqrt 3 x = x+18

x= 9(\sqrt3+1)

 

 

 


Option 1)

9(1+\sqrt3)

This is correct

Option 2)

18(1+\sqrt3)

This is incorrect

Option 3)

18(\sqrt3-1)

This is incorrect

Option 4)

9/2(\sqrt3-1)

This is incorrect

Posted by

Himanshu

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