Question

A LASER is a source of very intense, monochromatic, and unidirectional beam oflight. 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 preciselyusing a laser as a source of light. A laser light beamed at the Moon takes 2.56 s to return after reflection at the Moons surface. How much is the radius of the lunar orbit around the Earth ?

Answer 1

Time taken by the laser beam to return to Earth after reflection from the Moon $=2.56s$

Speed of light $=3\times {10}^{8}m/s$

Time taken by the laser beam to reach Moon $=1/2\times 2.56=1.28s$

Radius of the lunar orbit $=$ Distance between the Earth and the Moon

$=1.28\times 3\times {10}^8=3.84\times {10}^{8}m=3.84\times {10}^{5}km$