Question

In the late 1960's and 1970's the Apollo program landed many astronauts on the Moon. On one of

the trips the astronauts left a corner reflector. This is a special mirror which reflects light exactly in
the direction from where it came. This enabled scientists on Earth to determine the distance to the
Moon within a few centimeters. This is one of the most accurate measurements ever made between
the Earth and the Moon.
In one experiment, scientists on earth shone a laser beam onto the corner reflector and measured
how long it took for the beam to return to Earth. The time they measured was 2.63 seconds. How
many kilometers away was the moon at the time of the experiment?

Answer 1

"laser beam" can be handled as "light".

Speed of light in vacuum = 300,000 km/sec

Distance = (speed) x (time)

Distance light traveled = (300,000 km/sec) x (2.63 sec)

Distance the light traveled = 789,000 km

But this is DOUBLE the distance to the moon, because the laser light had to GO and COME BACK in order to be detected back on Earth.

So the distance to the moon was (1/2) of (789,000 km) = 394,500 km