# Speed of light homework

Q#1 : Mars and earth orbit the sun at radii of 228 million km and 150 million Km , respectively. when, in the future, your friend from Mars calls you on the phone and you answer "Hello" what are the minimum and maximum times you will have to wait for your friend to reply ?

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So what have you done so far? There's a template for a reason.

Dick
Homework Helper
What the maximum and minimum distances from Mars to Earth. T=D/V. Please at least try?

i did try:
2500x 10 ^9 /3x10^8(m/s) am i doing it the right way ?

Dick
Homework Helper
2500x10^9 what? Meters, km? Put units on your distance. And how did you get 2500 anyway?

oh hold on I made a mistake here, t supposed to be 228 million Km/3x10^8(m/s)

Dick
Homework Helper
Mars and Earth orbit on concentric roughly circular orbits around the sun. They can be either on the same side of the sun, in which case you would subtract the radiii, right? Or they could be on the opposite sides, in which case you would add them, yes? Draw a picture. But dividing distance by velocity is a good idea!

so I'm on the right track
and i thought that i needed to get delta radii, but then I've changed my mind.

Dick
Homework Helper
Now finish. Or are you done?

after getting the differences between the radii, I proceed and divide that number by the speed of light, right ? but when it says "million Km, does it mean #X10^9" ?

Dick
Homework Helper
1 million km=10^9 meters. 1km=10^3m. 1 million=10^6. If that's what you mean, yes.

ok, so this is how i get the minimum time : 78X10^9/3x10^8(m/s)= 260s
and the maximum : 378x10^9/3x10^8(m/s)= 1260s
so what do you think? am I correct?

yeah

yes, thank you all.