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Q. A light ray is incident on a plane mirror $M$ . The mirror is rotated in direction as shown in figure by an arrows at frequency $\left(\right.\frac{9}{\pi }\left.\right)$ revolution/sec. What will be the speed of the spot on wall when angle of incident becomes $37^\circ $ given that the light reflected by the mirror is received on the wall $W$ at a distance of $10m$ .
Question

NTA AbhyasNTA Abhyas 2020

Solution:


$1=10tan\left(\right.90-\theta \left.\right)\frac{dl}{dt}=10\left(cosec\right)^{2}\theta \times \omega =500m/sec$