Posted by **Beth** on Friday, July 20, 2012 at 5:20pm.

A spacecraft approaching the earth launches an exploration vehicle. After the launch, an observer on earth sees the spacecraft approaching at a speed of 0.74c and the exploration vehicle approaching at a speed of 0.98c. What is the speed of the exploration vehicle relative to the spaceship?

I keep getting .259 which is the wrong answer. I don't know what Im doing wrong I use the velocity addition formula but it never works. Please help!!

- Physics -
**drwls**, Friday, July 20, 2012 at 8:07pm
0.98c is the relative velocity of the probe with respect to the Earth (V3). That is the relativistic sum of the probe velocity (V2) with respect to the spaceship, and the spaceship with respect to Earth (V1).

V3 = (V1 + V2)/[1 + (V1*V2)/c^2]

You want to solve for V2.

I get V2 = 0.873c

- Physics -
**Beth**, Saturday, July 21, 2012 at 8:49pm
Thank you. i sort of had to back track to get the answer you got but eventually got it. Thank you!!

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