Swinburne University of Technology Faculty of Science, Engineering and Technology PHY20008 Physics 2B Special Relativity [45 marks total] Section A: Multiple Choice [5 questions for 10 marks total] Record your answers in the script book provided. 1 (a) The Michelson-Morley experiment showed: A : that the Earth's motion was slower than the speed of light B : evidence of unstable sub-atomic particles C : that matter and energy were interchangeable properties D : no evidence for the existence of the ether (b) I am in reference frame > and you are in a different frame, 2', that I measure to be moving in the x-direction with speed v relative to me. Which of the following will we both always agree upon? A : distances in the z-direction B : the relative speed of the two frames C : the speed of light travelling from a source moving relative to both of us D : all of the above (c) If information could be transmitted faster than the speed of light, one of the consequences would be A : the existence of negative energy B : the reversal of cause and effect C : violation of Newton's 2nd Law D : the creation of antimatter (Question 1 continues on the next page.) Final Exam, Semester 2 - 2015 Page 1 of 11
Swinburne University of Technology Faculty of Science, Engineering and Technology PHY20008 Physics 2B (d) Which of the following combinations of energy (E) and momentum (p) is a frame-invariant quantity (note; ) = 1 /1-B2 A : E2 - p2c2 B : Y(E - vp) C: E + pc D: /p -? (e) When using the Lorentz transformations to compare observations in different reference frames, the "observation time" for information to get to the observer is not included because A : measurements are always taken to be "local" (immediately adjacent to the event) B : the speed of light is so fast that transmission time is negligible C : all observers will agree on the speed of light D : this is already included as part of the "gamma" factor, Y Final Exam, Semester 2 - 2015 Page 2 of 11
Swinburne University of Technology Faculty of Science, Engineering and Technology PHY20008 Physics 2B Section B: [2 questions, worth a total of 35 marks] 2. A rocket ship of proper length 500 m is travelling past a space station with speed 0.8c relative to the station. From the front of the ship, a radio signal is sent back to the station In the frame of the ship, this signal happens to be emitted just as the rear of the ship passes the space station. [Treat this as a 1D problem, ignoring any displacements orthogonal to the motion.] (a) Calculate how far from the space station the front of the ship is (as measured by people in the ship) at the instant the station receives the radio signal. (b) Determine whether the people on the space station measure the signal to