JEE Main 2018MathematicsHeights and DistancesEasyMCQ

JEE Main 2018 — Heights and Distances Question with Solution

JEE Main 2018 (15 Apr)

Question

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

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Show full solutionCorrect option: D
Correct answer
D1440

Step-by-step explanation

Let from point C the angle of elevation of plane at B is 60°.

and after 5 seconds it reach at B'

In ∆ABC, AC=3cot60°=1

In ΔCA'B', A'C=3 cot30°=3

Hence, distance AA'=A'C-AC=3-1=2

Now, speed equals total distance travelled divided by total time taken.

Thus, speed =2560×60=2×60×605=72005=1440 km/hr

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About this question

This is a previous-year question from JEE Main 2018, covering the Heights and Distances chapter of Mathematics. PrepSharp catalogues every PYQ from JEE Main with a verified answer key and step-by-step solution prepared by IIT alumni — so you can search by chapter, topic or year and revise efficiently.