1. The problem statement, all variables and given/known data 2. Relevant equations Equations of motion: v = u + at s = 1/2 (u + v) t s = ut + 1/2at^2 v^2 = u^2 + 2as 3. The attempt at a solution Hello, on a i used the 2nd equation: 30m = 1/2 (3*10^8m/s+3*10^8m/s) t so -> t = 1*10^-7s but to get the correct solution i need to take t*2 i think. I made a small sketch to this question, but i dont really know why i need to take it times 2, is it because of sending and receiving the signal? I hope someone can explain this to me. b was a lot more confusion for me because of the two time values: first i used s = v*t s = 3*10^8m/s * 2.14 * 10^-7s so -> s = 64.2m this is where i get lost, so now i used the 2nd equation again with the other time value: 64.2m = 1/2 (0m/s + final velocity) * 0.1s so -> v (final velocity) = 1284 m/s so im pretty sure thats waaay to high, but i think the first part is correct. Thanks for every answer.