Skip to main content
Back to Height and Distance
JEE Main 2019
Height and Distance
Height and Distance
Medium

Question

A man is walking towards a vertical pillar in a straight path, at a uniform speed. At a certain point A on the path, he observes that the angle of elevation of the top of the pillar is 30 o . After walking for 10 minutes from A in the same direction, at a point B, he observes that the angle of elevation of the top of the pillar is 60 o . Then the time taken (in minutes) by him, from B to reach the pillar, is :

Options

Solution

According to given information, we have the following figure Now, from ACD\triangle A C D and BCD\triangle B C D, we have tan30=hx+y\tan 30^{\circ}=\frac{h}{x+y} and tan60=hy\tan 60^{\circ}=\frac{h}{y} h=x+y3...(i)\Rightarrow h=\frac{x+y}{\sqrt{3}}\quad...(i) and h=3y...(ii)h=\sqrt{3} y\quad...(ii) From Eqs. (i) and (ii), x+y3=3yx+y=3y\frac{x+y}{\sqrt{3}}=\sqrt{3} y \Rightarrow x+y=3 y x2y=0y=x2\Rightarrow x-2 y=0 \Rightarrow y=\frac{x}{2} \because Speed is uniform. \therefore Distance yy will be cover in 5 min5 \mathrm{~min}. \because Distance xx covered in 10 min10 \mathrm{~min}. \therefore Distance x2\frac{x}{2} will be cover in 5 min5 \mathrm{~min}.

Practice More Height and Distance Questions

View All Questions