Questions: 1. Give two examples of inertial and non inertial reference frames. 2
ID: 2108159 • Letter: Q
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Questions: 1. Give two examples of inertial and non inertial reference frames. 2. A woman stands on a moving railroad car. She slips and her ice cream cone flies straight up into the air. Neglecting air resistance, will it land on her, behind her, or in front of her? 3. In view of the 1st postulate of special relativity does the earth really move around the sun, or is it just as valid to say that the sun goes around the earth? 4. If you were on a space ship traveling at 0.5c away from a star, at what speed would the starlight pass you? 5. Will two events occurring at the same place and time for one observer be simultaneous for a second observer moving with respect to the first? 6. Does time dilation imply that time actually passes more slowly from the point of view of the people in moving reference frames? Explain. 7. Today's subway trains are said to age people prematurely. Suppose in the future we could construct trains that traveled near the speed of light, how would this affect the aging process? 8. A young woman astronaut has just arrived home from a space voyage. She rushes to an old, gray-haired man and in the ensuing conversation she refers to him as her son! How might this be possible? 9. If you were traveling at 0.5c away from the earth would you notice a change in your heartbeat? Would your height, mass, or waistline change? How would observers on earth describe you (be specific)? 10. Do mass increase, time dilation, and length contraction occur at normal speeds (~100 mph)? Explain. 11. Explain the statement, “The sun is losing mass†according to special relativity? 12. Explain the concepts of rest mass and rest energy. Problems: 1. An astronaut travels at 0.93c. As one hour passes for her how much time passes for an observer on earth? 2. A spaceship passes you at 0.9c. You note its length to be 80.0 m. How long is it when at rest? 3. At what speed will an object's mass be twice its rest mass? 4. Ideally, how much energy could be obtained from a 500 g golf ball? How long could that energy run a 150 W light bulb (remember, P=E/t)? 5. Two dragsters approach each other in a game of "chicken" at 80 mph, what is the speed of each with respect to the other? Two space dragsters play a similar game at much higher speeds, they approach each other at speeds of 0.6c. What speed is each going with respect to the other? 6. The nearest star, Proxima Centauri, is 4.3 light years away. How fast would you have to go to make the trip seem like a distance of 1000 km? One light year is approximately equal to 9.5 x 1012 km. 7. A farm boy studying physics believes he can get a 12-m-long pole into a 10-m-long barn if he runs fast enough (carrying the pole of course). Can he do it? Explain. How does your answer deal with the fact that when he is running the barn looks even shorter to him? Questions: 1. Give two examples of inertial and non inertial reference frames. 2. A woman stands on a moving railroad car. She slips and her ice cream cone flies straight up into the air. Neglecting air resistance, will it land on her, behind her, or in front of her? 3. In view of the 1st postulate of special relativity does the earth really move around the sun, or is it just as valid to say that the sun goes around the earth? 4. If you were on a space ship traveling at 0.5c away from a star, at what speed would the starlight pass you? 5. Will two events occurring at the same place and time for one observer be simultaneous for a second observer moving with respect to the first? 6. Does time dilation imply that time actually passes more slowly from the point of view of the people in moving reference frames? Explain. 7. Today's subway trains are said to age people prematurely. Suppose in the future we could construct trains that traveled near the speed of light, how would this affect the aging process? 8. A young woman astronaut has just arrived home from a space voyage. She rushes to an old, gray-haired man and in the ensuing conversation she refers to him as her son! How might this be possible? 9. If you were traveling at 0.5c away from the earth would you notice a change in your heartbeat? Would your height, mass, or waistline change? How would observers on earth describe you (be specific)? 10. Do mass increase, time dilation, and length contraction occur at normal speeds (~100 mph)? Explain. 11. Explain the statement, “The sun is losing mass†according to special relativity? 12. Explain the concepts of rest mass and rest energy. Problems: 1. An astronaut travels at 0.93c. As one hour passes for her how much time passes for an observer on earth? 2. A spaceship passes you at 0.9c. You note its length to be 80.0 m. How long is it when at rest? 3. At what speed will an object's mass be twice its rest mass? 4. Ideally, how much energy could be obtained from a 500 g golf ball? How long could that energy run a 150 W light bulb (remember, P=E/t)? 5. Two dragsters approach each other in a game of "chicken" at 80 mph, what is the speed of each with respect to the other? Two space dragsters play a similar game at much higher speeds, they approach each other at speeds of 0.6c. What speed is each going with respect to the other? 6. The nearest star, Proxima Centauri, is 4.3 light years away. How fast would you have to go to make the trip seem like a distance of 1000 km? One light year is approximately equal to 9.5 x 1012 km. 7. A farm boy studying physics believes he can get a 12-m-long pole into a 10-m-long barn if he runs fast enough (carrying the pole of course). Can he do it? Explain. How does your answer deal with the fact that when he is running the barn looks even shorter to him?Explanation / Answer
The motion of a body can only be described relative to something else - other bodies, observers, or a set of space-time coordinates. These are called frames of reference. If the coordinates are chosen badly, the laws of motion may be more complex than necessary. For example, suppose a free body (one having no external forces on it) is at rest at some instant. In many coordinate systems, it would begin to move at the next instant, even though there are no forces on it. However, a frame of reference can always be chosen in which it remains stationary. Similarly, if space is not described uniformly or time independently, a coordinate system could describe the simple flight of a free body in space as a complicated zig-zag in its coordinate system. Indeed, an intuitive summary of inertial frames can be given as: In an inertial reference frame, the laws of mechanics take their simplest form.[1] In an inertial frame, Newton's first law (the law of inertia) is satisfied: Any free motion has a constant magnitude and direction.[1] Newton's second law for a particle takes the form: with F the net force (a vector), m the mass of a particle and a the acceleration of the particle (also a vector) which would be measured by an observer at rest in the frame. The force F is the vector sum of all "real" forces on the particle, such as electromagnetic, gravitational, nuclear and so forth. In contrast, Newton's second law in a rotating frame of reference, rotating at angular rate ? about an axis, takes the form: which looks the same as in an inertial frame, but now the force F? is the resultant of not only F, but also additional terms (the paragraph following this equation presents the main points without detailed mathematics): where the angular rotation of the frame is expressed by the vector ? pointing in the direction of the axis of rotation, and with magnitude equal to the angular rate of rotation ?, symbol
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