Physics repost
posted by Mary .
I apologise for reposting this question but it is still not working out for me.
I know that:
speed of light c=3.0x10^8
Time interval delta t=0.19x10^9s
The relationship between actual time and roudtrip distance is
d=ct
Also if there is and uncertainty of delta time, then it introduces an uncertainty of delta distance
ie d+delta d = c(t + delta t)
Knowing all of this I still don't understand how to work out the problem. I am continuosly coming up with the incorrect answer. please help!
Question:
The distance between earth and the moon can be determined from the time it takes for a laser beam to travel from earth to a reflector on the moon and back. If the roundtrip time can be measured to an accuracy of 0.19 of a nanosecond (1 ns = 109 s), what is the corresponding error in the earthmoon distance?

The Earth moon distance is d, and the roundtrip travel time is
t = 2 d/ c
d = (c/2) t
delta d = 1.5*10^8 m/s * (delta t)
= 0.19*10^9 s *(1.5*10^8 m/s) = 2.9*10^2 m = 2.9 cm
(about one inch)