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Unformatted text preview: Chapter 26 Relativity Quick Quizzes 1. (a). Less time will have passed for you in your frame of reference than for your employer back on Earth. Thus, to maximize your paycheck, you should choose to have your pay calculated according to the elapsed time on a clock on Earth. 2. No. Your sleeping cabin is at rest in your reference frame, thus, it will have its proper length. There will be no change in measured lengths of objects within your spacecraft. Another observer, on a spacecraft traveling at a high speed relative to yours, will claim that you are able to fit into a shorter sleeping cabin (if your body is oriented in a direction parallel to your direction of travel relative to the other observer). 3. (a), (e). The outgoing rocket will appear to have a shorter length and a slower clock. The answers are the same for the incoming rocket. Length contraction and time dilation depend only on the magnitude of the relative velocity, not on the direction. 4. (a) False (b) False (c) True (d) False A reflected photon does exert a force on the surface. Although a photon has zero mass, a photon does carry momentum. When it reflects from a surface, there is a change in the momentum, just like the change in momentum of a ball bouncing off a wall. According to the momentum interpretation of Newtons second law, a change in momentum results in a force on the surface. This concept is used in theoretical studies of space sailing. These studies propose building non-powered spacecraft with huge reflective sails oriented perpendicularly to the rays from the Sun. The large number of photons from the Sun reflecting from the surface of the sail will exert a force which, although small, will provide a continuous acceleration. This would allow the spacecraft to travel to other planets without fuel. 5. (a). The downstairs clock runs more slowly because it is closer to Earth and hence experiences a stronger gravitational field than the upstairs clock does. 107 108 CHAPTER 26 Answers to Even Numbered Conceptual Questions 2. To be strictly correct, the equation should be written as 2 E mc = where ( 29 2 1 1 v c =- . When the object is at rest 0 and 1 v = = , so the equation reverts to the popular form 2 E mc = . When v , 2 R E E mc = and the difference ( 29 2 1 R KE E E mc =- =- accurately accounts for the kinetic energy of the moving mass. 4. The two observers will agree on the speed of light and on the speed at which they move relative to one another. 6. Special relativity describes inertial reference frames -- that is , reference frames that are not accelerating. General relativity describes all reference frames. 8. You would see the same thing that you see when looking at a mirror when at rest. The theory of relativity tells us that all experiments will give the same results in all inertial frames of reference....
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- Spring '08