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DunWorry
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Homework Statement
A spacecraft S2 is capable of firing a missile which can travel 0.98c. S2 is escaping from S1 at a speed of 0.95c when it fires a missile towards S1.
part A) According to the pilot of S2, what speed does the missile approach S1?
Part B) according to pilot of S1, what speed does the missile approach it?
Homework Equations
Call the S1 frame x and S2 frame y and speed of missile U
Velocity addition V[itex]_{x}[/itex] = [itex]\frac{v_{y} + U}{1 + \frac{v_{y} U}{C^{2}}}[/itex]
The Attempt at a Solution
My problem lies with part A. The answer is just a simple 0.98c - 0.95c = 0.03c. However I can't get this result with the velocity addition formula, why is it in this case the velocity addition formula does not work/ does not apply?
I tried imagining S2 moving to right (positive) and firing the missile backwards towards S1 (left direction which is negative). Taking the frame of reference of S2, the spaceship S2 is stationary and S1 is moving to the left at a velocity of -0.95c, the missile is also moving to left with speed -0.98c
if I try use the velocity addition formula Velocity addition V[itex]_{x}[/itex] = [itex]\frac{-0.98 - 0.95}{1 + \frac{0.98 x 0.95}{C^{2}}}[/itex] I get -0.9994C, which is wrong. The answer is just 0.98c - 0.95C but I cannot see what I am doing wrong with the velocity addition formula or why it is not needed in this case.
I solved part B) using the formula V[itex]_{x}[/itex] = [itex]\frac{0.98 - 0.95}{1 - \frac{0.98 x 0.95}{C^{2}}}[/itex]. The signs are as they are as in the frame of S1, the ship S2 is moving in + direction with speed 0.98C and the missile is moving with -0.95C. It seems to work for part B but not for part A and I cannot see why.
Thanks