The mirror of length L moves horizontally as shown in the figure with a velocity v. The mirror is illuminated by a point source of light 'P' placed on the ground. The rate at which the length of the light spot on the ground increases is - |
A) v
B) zero
C) 2v
D) 3v
Correct Answer: B
Solution :
\[{{V}_{A}}=\frac{d}{dt}(2vt)=2v;{{v}_{B}}=\frac{d}{dt}(2vt+2L)=2v\] |
\[\Rightarrow {{v}_{A}}={{v}_{B}}\] |
\[\therefore \]Length of AB will remain same. |
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