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JEE Main 2019
Height and Distance
Height and Distance
Medium

Question

The angle of elevation of the top P\mathrm{P} of a tower from the feet of one person standing due South of the tower is 4545^{\circ} and from the feet of another person standing due west of the tower is 3030^{\circ}. If the height of the tower is 5 meters, then the distance (in meters) between the two persons is equal to

Options

Solution

Let's denote the person standing due south as S and the one standing due west as W. Also, let the tower be at point T. From person S's perspective, we have a right triangle SPT\triangle SPT. The height of the tower PT is given as 5m, which is the opposite side for angle S. The angle at S is 4545^\circ. From the tangent trigonometric ratio, we have : tan45=PTST=5ST\tan{45^\circ} = \frac{PT}{ST} = \frac{5}{ST} Since tan45=1\tan{45^\circ}=1, we get ST=5ST = 5m. Similarly, from person W's perspective, we have a right triangle WPT\triangle WPT. The angle at W is 3030^\circ. From the tangent trigonometric ratio, we have: tan30=PTWT=5WT\tan{30^\circ} = \frac{PT}{WT} = \frac{5}{WT} Since tan30=13\tan{30^\circ}=\frac{1}{\sqrt{3}}, we get WT=53WT = 5\sqrt{3}m. Since S and W are perpendicular to each other (one is due south and the other is due west), SWT\triangle SWT forms a right triangle. We can find SWSW (the distance between the two people) using the Pythagorean theorem: SW2=ST2+WT2=52+(53)2=25+75=100SW^2 = ST^2 + WT^2 = 5^2 + (5\sqrt{3})^2 = 25 + 75 = 100 So, SW=100=10SW = \sqrt{100} = 10m. Hence, the correct answer is 10 meters, which corresponds to Option A.

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