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Physics for Engineers - 1
The Relativistic Addition Of Velocity
Thus any velocity relativistically added to c gives a resultant value c. In this sense, c plays the same role in relativity that an infinite velocity in classical case.
Let us calculate the velocities perpendicular to the relative motion of frames. Let 
and 
are the positions of the body at 
and 
in 
system. So the velocity in 
system is,
We can use Lorentz transformation for the calculation of corresponding velocities in 
frame.
We can write the corresponding inverse transformation by changing 
to -,
