Physics - Geometrical Optics Question with Solution | TestHub

PhysicsGeometrical OpticsReflection at plane surfaceMedium2 minQB

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One night, a boy of height $h = 1.5 m$ is standing on the bank of a straight canal, on the other bank of which a lamp is installed at a height $H = 6 m$ on a pole. There are no ripples on the water surface so light emanated from the lamp, appears as a flare (bright spot) after reflection from the water surface. When the boy starts walking along the bank, the flare appears to him moving at a constant speed $u = 3 m / s$ relative to the ground. Find speed of the boy. (in m/s)

If answer is $\frac{x}{y}$ write value of $x + y$

Answer:

Solution:

$\frac{x}{x ^{'}} = \frac{FF ^{'}}{BB ^{'}} = \frac{LF ^{'}}{LB ^{'}} = \frac{H}{H + h} = \frac{4}{5} \Rightarrow \frac{dx ^{'}}{dt} = \frac{5}{4} \frac{dx}{dt} = \frac{5}{4} \times 3 = 3.75 m / s$

Stream:JEESubject:PhysicsTopic:Geometrical OpticsSubtopic:Reflection at plane surface

⏱ 2mℹ️ Source: QB

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