How long (in seconds) does it take for a radio wave of frequency 8.94 × 106 s–1 to reach Mars when Mars is 8.2 × 107 km from Earth?

2 Answers
Jan 26, 2016

I found: t=0.27s

Explanation:

You radio wave should travel at the speed of light in vacuum c=3xx10^8m/s
so basically it would take (velocity=distance/time rearranged):
t=d/c=(8.2xx10^10)/(3xx10^8)=273s to reach Mars.

Jun 20, 2018

270 sec. (=4 min. 30 sec.)

Explanation:

Any radio wave is moving at the speed of light, regardless of the frequency, so the frequency should be superfluous information.

The speed is light is close to 300,000 (km)/s
I take the distance you are given, to be 8.2*10^7 km (since 8.2*107 km doesn't make good sense - it's less than 1000 km)
i.e. 82,000,000 km.

Before we actually compute this, we can notice that this is a little more than half the distance of the earth from the sun (150 mill. km), a distance the light uses 500 sek. = 8 min 20 sec. to travel, so we should get about 4 1/2 min for the radio wave to reach Mars from the earth.

Actual calculation:
(82,000,000 km)/(300,000 (km)/s)=820/3 s =273.3 s

As the distance is given with 2 significant figures, we round this off to 270 sek = 4 min 30 sec.