A) \[0.4\text{ }m/sec\]
B) \[0.8\text{ }m/sec\]
C) \[1.2\text{ }m/sec\]
D) None of these
Correct Answer: B
Solution :
\[\frac{dy}{dt}=1.2\]. According to the figure \[\frac{4.5}{1.8}=\frac{x+y}{x}\] \[\frac{5}{2}=\frac{x+y}{x}\Rightarrow 3x=2y\] |
\[x=\frac{2}{3}y\Rightarrow \frac{dx}{dt}=\frac{2}{3}\frac{dy}{dt}\] |
\[\therefore \] required rate of length of shadow \[\frac{dx}{dt}=0.8m/s.\] |
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