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Homework Help: Special Relativity - apparent speed

  1. Dec 17, 2008 #1
    1. The problem statement, all variables and given/known data

    I'm at rest. Someone in a space ship is approaching me at a speed of 0.8c.

    What speed do I see this person approaching me?
    Last edited: Dec 17, 2008
  2. jcsd
  3. Dec 17, 2008 #2
    What do you think the answer is? Do you have any formulas?

    Also, consider the scenario where you are traveling toward the spaceship with a speed of 0.8c as well. Since you are traveling at constant velocity, you can claim that you are at rest. What speed is the spaceship approaching toward you now?
  4. Dec 17, 2008 #3


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    You said "someone is approaching me at 0.8c". Then you asked "what speed do I see this person approaching me"? That doesn't even need relativity in any sense. They are the same question.
  5. Dec 17, 2008 #4
    Let's make him think a little bit. =)
  6. Dec 17, 2008 #5


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    If you think that's useful, ok. Geez. eprparadox? I think formulas are useless here.
  7. Dec 18, 2008 #6
    I apologize to all who viewed this thread! There was more to this question and I phrased it incorrectly from the beginning anyways. I also had included formulas and an attempt to solve the problem, but for some reason it wasn't posted. I think I may have accidentally selected a portion of the text and deleted it before confirming the thread.

    I'm an idiot, for sure. But not THAT big of an idiot!

    But thanks anyways for the responses. That's awful kind of you guys.
  8. Dec 18, 2008 #7
    Do you understand how an observer interprets velocity using special relativity? Based on your question (at least the part that is given), it seems you need help and I wanted to offer a few scenarios to make things clearer.
  9. Dec 18, 2008 #8

    First, thank you so much for your following up to my last post. I definitely do need help with this material. And it speaks volumes about the type of person you are that you would take the time to have a dialogue with me.

    Now with that in mind, I think it would be best for me to first grapple some more with this subject. At this point, my questions would be superficial at best. I don't think I've given myself the best chance to learn the material and I think sometimes I'm too quick to post a question on this forum because I know I'll get a response. But once I've gotten to a certain point where I feel more comfortable, I would love to hear your explanations and ideas. I hope your offer will still stand in a few weeks.

    Thank you again very much. I hope to speak with you soon.
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