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This is chapter 37 problem number 56.
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We have two protons that we know that are moving away from each other.
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So if we're going to call the speed v for one, the other one is going to be negative u.
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In the frame of each proton, the other appears to have the speed of 0 .7c.
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So this is actually u prime.
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It's going to be 0 .7c for us.
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As we know, u prime is going to be equal to u minus v.
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Over 1 minus uv over c squared.
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We're after v or negative u in this case.
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That's what's asked.
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So let's find everything in terms of v.
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So v is negative u, right? so then negative v, negative minus v is going to be one plus because you times v is already negative.
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One more negative makes it plus v squared over c squared.
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So negative 2v over 1 plus v squared over c squared is given to us as 0 .7 times c.
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Now, what we should do is, so then negative 2v equals to 1 plus v squared over c squared, we multiply both sides of this equation by denominator.
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Is going to be 0 .7c.
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Right? now if you divide both sides by c, these are going to cancel out...