Question

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 Moon to be 3.84 ✕ 108 m. Assume that the Moon is directly overhead and do not neglect the sizes of the Earth and Moon. (Assume the radius of the Earth and the Moon are 6380 km and 1740 km respectively.)

Answer 1

The speed of light is
`3 * 10^(8) (m)/(s)`

Step-by-step explanation:

Given:

Time interval of reflect light from panel
`t = 2.51` sec

Center to center distance between earth and moon
`x' = 3.84 * 10^(8)` m

Here light reflect from surface so net distance is given by,

`= 3.84 * 10^(8) - 6380000 -1740000`

`= 375884500` m

And light is reflect from moon surface,

`= 2 * 375884500`

`x = 751769000` m

So velocity is given by,

`v = (x)/(t)`

`v = (751769000)/(2.51)`

`v = 3 * 10^(8) (m)/(s)`

Therefore, the speed of light is
`3 * 10^(8) (m)/(s)`