Asked Dec 25, 2019

During the Apollo XI Moon landing, a retroreflecting panel
was erected on the Moon’s surface. The speed of light
can be found by measuring the time it takes a laser beam
to travel from Earth, reflect from the panel, and return to
Earth. If this interval is found to be 2.51 s, what is the measured
speed of light? Take the center - to - center distance
from Earth to the Moon to be 3.84 x 108 m. Assume the
Moon is directly overhead and do not neglect the sizes of
Earth and the Moon.


Expert Answer

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The total distance travelled by the light is, Ad = 2 (Dcenter to center - REarth - RMoon) Dcenter to center is the distance between the centers REarth is the radius of the Earth RMoon is the radius of the Moon Substitute 3.84 × 10° m for D center to center, 6.38 × 10° m for REarth and 1.76 x 106 m for RMoon. Ad = 2 (3.84 x 10® m – 6.38 × 10® m – 1.76 × 106 m) = 7.52 x 10° m The measured speed of light is, Ad Av = 44 At


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