Answer
1.25 s
Work Step by Step
Sound waves cannot travel in vacuum, so astronaut voices cannot reach Earth by the normal means. We assume the question means how long will it take for a television/radio signal to travel to the Earth carrying the astronaut’s voices.
Use the relationship d = vt and solve for the time.
Use d = the Earth–Moon distance (from the inside front cover), $d_{moon/Earth}=384\times10^{6}m $.
To be more accurate, subtract the Earth’s radius and Moon’s radius from this distance because the astronauts and the radio receivers are on the near sides of the moon and of the Earth.
$d_{revised}=384\times10^{6}m-6.38\times10^{6}m -1.74\times10^{6}m $
$$t=\frac{d}{v}=\frac{ d_{revised}}{3.00\times10^8m/s}=1.25s$$
