Two rockets A and B are moving away from the earth in opposite directions at 0.85c and -0.75c respectively.
How fast does A measure B to be travelling?
Now I have worked out v = -0.85-0.75/(1- -0.85*-0.75) = -0.997. This is correct.
Now I would like to work it out backwards to check my understanding so:
According to A:
B travels at 0.997c
The earth frame travels at 0.75c
Q - How fast does the earth measure B to be travelling?
The Attempt at a Solution
I expected the answer to be 0.85c but:
v=0.997-0.75/(1- 0.997*0.75) == 0.979 and not 0.85.
Thanks for any help