I am trying to understand a section in a textbook I have regarding Special Relativity, specifically deriving an expression for what is known as "relativistic mass", in order to find an expression for "relativistic momentum". I have attached the pages in the book which are giving me trouble, more specifically, the paragraph I have highlighted in red. I understand everything before that, however I can't seem to understand what the paragraph is saying.(adsbygoogle = window.adsbygoogle || []).push({});

I have derived an expression for the Lorentz Velocity Transformation so I understand where the author is getting at, just don't exactly recognize how the numerator of the transformation equation is 2u assuming my derived expression is:

[tex]v_x=\frac{v_x^{'}+u}{1+\frac{u v_x^'}{c^2}}[/tex]

Can somebody restate what he is saying in the highlighted paragraph?

[PLAIN]http://people.tamu.edu/~malindenmoyer/tamu/special_relativity.png [Broken]

Reference:

Taylor, J. G. Special Relativity. Oxford: Clarendon, 1975. Print.

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# Homework Help: Special Relativity - Relativistic Dynamics

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