JEE Main 2021MathematicsHeights and DistancesEasyMCQ

JEE Main 2021 — Heights and Distances Question with Solution

JEE Main 2021 (25 Feb Shift 1)

Question

A man is observing, from the top of a tower, a boat speeding towards the tower from a certain point A, with uniform speed. At that point, angle of depression of the boat with the man's eye is 30° (Ignore man's height). After sailing for 20 seconds, towards the base of the tower (which is at the level of water), the boat has reached a point B, where the angle of depression is 45°. Then the time taken (in seconds) by the boat from B to reach the base of the tower is :

Choose an option

Show full solutionCorrect option: D
Correct answer
D10(3+1)

Step-by-step explanation

Let speed of boat is u m/s and height of tower
is h meter & distance AB=x metre

∴x=hcot30°-hcot45°

⇒x=h(3-1)

∴u=x20=h(3-1)20 m/s

∴ Time taken to travel from B to C (Distance
=h meter)

=hu=hh(3-1)20=203-1=10(3+1)sec .

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About this question

This is a previous-year question from JEE Main 2021, 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.