Rocket ship speed and relativity

[cragar]

ok I know that nothing with mass can travel at c but i have to ask this question.
if I am in a rocket ship traveling at .5c and another rocket ship is traveling at .5c in the opposite direction then am I traveling at c relative to him . Probably Galilean transformations don’t work in this situation and I am probably missing something can you guys help me out.

 

[Eric McClean]

Now I don't have its answer but I will tell you as I get an adequate amount of time.

 

[modulus]

Well, I was reading in another thread that nothing actually has an absolute mass. It depends on which force you're considering (that is applied on that mass). for example, a nuetron's gravitational mass and nuclear mass may have slightly different values.

I think the same thing goes here. The guy in the other rocket ship will percieve you as a massless entity, but, somebody who is stationary wrt both of you, will not.

Just a fleeting thought... I haven't verified this from anywhere.

 

[Doc Al]

ok I know that nothing with mass can travel at c but i have to ask this question.
if I am in a rocket ship traveling at .5c and another rocket ship is traveling at .5c in the opposite direction then am I traveling at c relative to him . Probably Galilean transformations don’t work in this situation and I am probably missing something can you guys help me out.

You are correct that Galilean transformations don't work with such high speeds. You need to use relativistic velocity addition (derived from the Lorentz transformations):

[tex]
V_{a/c} = \frac{V_{a/b} + V_{b/c}}{1 + (V_{a/b} V_{b/c})/c^2}
[/tex]

The speed of the other rocket with respect to you will be 0.8c, not c.

 

[cragar]

thanks for the answer .

 

[Zula110100100]

Would a stationary observer see them coming together at a rate of c?

 

[Janus]

Would a stationary observer see them coming together at a rate of c?

Yes. This is called the "closing velocity".