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A LASER is a source of very intense, monochromatic, and unidirectional beam of light. These properties of a laser light can be exploited to measure long distances. The distance of the Moon from the Earth has been already determined very precisely using a laser as a source of light. A laser light beamed at the Moon takes 2.56 s to return after reflection at the Moon's surface. How much is the radius of the lunar orbit around the Earth?

$\begin {array} {1 1} (A)\;3.84 \times 10^5 km & \quad (B)\;38.4 \times 10^5 km \\ (C)\;3.84 \times 10^9 km & \quad (D)\;38.4 \times 10^9 km \end {array}$

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Ans : (A)
$3.84 \times 10^5 km $
answered May 28, 2014 by thanvigandhi_1