JEE Mains · Maths · STD 11 - Trigonometrical equations
An aeroplane flying at a constant speed, parallel to the horizontal ground, \(\sqrt 3\, km\) above it, is observed at an elevation of \(60^o\) from a point on the ground. If, after five seconds, its elevation from the same point, is \(30^o\), then the speed (in \(km/hr\)) of the aeroplane is
- A \(1500\)
- B \(750\)
- C \(720\)
- D \(1440\)
Answer & Solution
Correct Answer
(D) \(1440\)
Step-by-step Solution
Detailed explanation
For \(\Delta OA,\,\,A,\,O{A_1}\, = \,\frac{{\sqrt 3 }}{{\tan \,\,{{60}^o}}}\, = \,1\,km\) For \(\Delta O{B_1},\,\,B,\,O{B_1}\, = \,\frac{{\sqrt 3 }}{{\tan \,\,{{60}^o}}}\, = \,3\,km\) As, a distance of \(3-1=2\,km\) is covered in \(5\,seconds\). Therefore the speed of the plane…
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