# Speed of light

1. Apr 8, 2008

### louie3006

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 ?

2. Apr 8, 2008

### Snazzy

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

3. Apr 8, 2008

### Dick

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

4. Apr 8, 2008

### louie3006

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

5. Apr 8, 2008

### Dick

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

6. Apr 8, 2008

### louie3006

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

7. Apr 8, 2008

### Dick

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!

8. Apr 8, 2008

### louie3006

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

9. Apr 8, 2008

### Dick

Now finish. Or are you done?

10. Apr 9, 2008

### louie3006

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" ?

11. Apr 9, 2008

### Dick

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

12. Apr 9, 2008

### louie3006

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?

13. Apr 9, 2008

yeah

14. Apr 9, 2008

### louie3006

yes, thank you all.

15. Apr 9, 2008

### Snazzy

Actually, when you reply 'hello', your message has to get there, and the reply has to come back before you can hear your friend's reply.