transform.Polar will appear below in a Java enabled browser.

The above applet will solve problems related to relativity.  When you input the x-position, T(time),

and velocity of the other observers, then the applet will tell the new x-position and time.

****Warning*****

Only enter in values that are greater than or equal to zero or less than or equal to one for velocity.

This is because velocity is relative to the speed of light (which in this case is 1).

Documentation