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JEE Main201815 Apr 2018Morning ShiftMathematicsHeights and DistancesActual

An aeroplane flying at a constant speed, parallel to the horizontal ground, 3 ~km above it, is observed at an elevation of 60^ from a point on the ground. If, after five seconds, its elevation from the same point, is 30^ , then the speed (in km / hr ) of the aeroplane is

Options

  1. A1500
  2. B750
  3. C720
  4. D1440

Correct answer

D. 1440

Step-by-step solution

For OA , A , OA ₁= 3 60^ =1 ~km For OB ₁, ~B , OB ₁= 3 30^ =3 ~km . As, a distance of 3-1=2 ~km is covered in 5 seconds. Therefore the speed of the plane is 2 3600 5 =1440 ~km / hr

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