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Homework Help: Relativity question

  1. Nov 9, 2009 #1
    At first , I shoul say : I am sorry , just now i posta a question , but my answer is aplly other question. I have edited it now.

    1) If you were standing upright, facing forward but moving at a relativistic velocity to your right, which of the following quantities would change : height, width , pulse rate, number of atoms in my body, mass , temperature, rate of ageing, girth (waistline), or net electrical charge ?

    : I think the mass, width ,pulse rate and rate ageing are changed. rate ageing chage , I take the reason is twin paradox.

    2) As the head traffic engineer for the department of highways, you are in charge of setting a safe but fuel-efficient speed limit on cars. Calculate a speed limit using relativistic equations and explain your reason for your choice of speed limit. Keep in mind that collisions cause changes in kinetic energy.

    : My idear is v=s/t, in the relativity, t own two value, one is relativety time, one is proper time, but the s also have two value, so how can i think this question ? Please give me some idea or remind.

    3)Assume light speed is 30m/s in our world, Aliens visiting your planet from another quadrant of the galaxy, where the speed of light is 3*10^8 m/s,say your food seems relatively cold. Explain.

    : I think , because aliens world ,light speed is so fast, they look our world is slowly. as we cook hot food , because their time is fast, the food is cold.

    P.S. : last question , I lose a condition , is light speed is 30 m/s in our world. all of these question is in a relativity thought experiment . Please help me check these answer again. Thanks very much.
    Last edited: Nov 9, 2009
  2. jcsd
  3. Nov 9, 2009 #2
    Okay if I get what you're saying you seem to have the idea for the first part. On the second part I don't really don't understand what you're saying for you're Idea. For the third part think about the rest energy equation... to them the rest energy would be negligable. Also the speed of light is not 30 m/s it is 300000000 m/s or 3.0x10^8 m/s
  4. Nov 9, 2009 #3
    Thanks,I will do the question 2 again , I will try to write a clear dear.
  5. Nov 9, 2009 #4


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    I think you have the right idea, but develop it further. What causes food to be hot? What's the maximum possible speed if the speed of light is 30 m/s?
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