Question
A laser light bean sent to the moon takes 2.56s to return after reflection at the Moon's surface. Calculate the radius of the lunar orbit around the earth.
✓
Answer
Radius of the lunar orbit around the earth = Distance between the moon and the earth. Time taken by the laser beam from earth to moon and then back to the earth = 2.56s. $\therefore$ Time taken by the laser beam to go from earth to the moon is $\text{t}=\frac{2.56}{2}=1.28\text{s}$ Speed of the laser beam (i.e. light) $\text{c}=3\times10^8\text{ms}^{-1}$ $\therefore$ Distance between moon and earth, $\text{S}=\text{ct}=3\times10^8\times1.28$ $=3.84\times10^8\text{m}=3.84\times10^5\text{km}$Ms Distance between moon and earth,
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