Chapter 27, Problem 64A

Consider a pulse of laser light aimed at the moon that bounces back to Earth. The distance between Earth and the moon is $3.8\times {10}^{8}m$.

a. Show that the round-trip time for the light is 2.5 seconds.

b. Why does an astronaut on the moon have to be patient in talking with Mission Control on Earth?

To determine

Show that the round-trip time for the light is 2.5 seconds.

Answer to Problem 64A

The round-trip time is 2.5 s.

Explanation of Solution

Given data:

Distance between earth and the moon(d ) = 3.8×10⁸ m.

Formula used:

Time, $t=2\times \frac{d}{c}$ s.

Calculation:

The round trip means the signal moves from one region and it bounces back to the same region. So, it is necessary to multiply with constant parameter 2.

We know that, the speed of light c =3×10⁸m/s.

Substituting the values in the equation of time ‘t’ is,

  $=2\times \frac{3.8\times {10}^{8}m}{3\times {10}^{8}m/s}$ s

= 2.53s.

= 2.5s.

Conclusion:

It’s shown that the time takes for the round-trip is 2.5s.

To determine

Explain the astronaut should be patient in talking with machine control on earth.

Explanation of Solution

Introduction:

The moon is approximately 350 km away from the earth. And there should be delay in communication.

The moon is approximately 350 km away from the earth and the communications between the Earth and the Moon have some considerable delay.

If the astronaut on the moon wants to communicate with ground control, he needs a patience, because there would be delay in communication about 2.2 seconds to 2.5 seconds. On average it is 2.5 seconds.

Conclusion:

The astronaut on the moon should be patient for 2.5 seconds while communicating with ground control.