15: Velocity transformation and length contraction:) As usual, consider two reference frames S : (x, y, z, t) and S' : (x', y', z', t'), with S' moving in the +x direction at speed v with respect to S, and with origins coinciding at times t = t' = 0. A rod of proper length Lo oriented parallel to the x' axis moves along the x' direction with speed u' with respect to the S' frame. Q15a: What is the rod's length as measured by an observer in the S frame? Hint: First find the speed of the rod in the S frame. Then use that speed to find the length in the S frame.