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My speed?

  1. Jan 17, 2009 #1
    What speed am I traveling at when I am run at the top a moving train.(Assuming train is going at 10 km/hr and I am running at 2km/hr)

    Sriram
     
  2. jcsd
  3. Jan 17, 2009 #2

    HallsofIvy

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    Classical Physics:
    If you are on a train going 10 km/hr, relative to the ground, and you are running at 2 km/hr relative to the train, toward the front of the train, then your speed relative to the ground is 10+2= 12 km/hr. If you are running toward the back of the train, your speed relative to the ground is 10-2= 8 km/hr.

    Relativity:
    If you are on a train going 10 km/hr, relative to the ground, and you are running at 2 km/hr relative to the train, toward the front of the train, then your speed relative to the ground is [itex] (10+2)/(1+ (10)(2)/c^2[/itex]= [itex](10+2)/(1+ 20/( 299,792,458)^2[/itex] which, even to 12 decimal place accuracy, the limit of my calculator, 12.000000000000 km/hr. Similarly, if you are running toward the back of the train, your speed is still 8 km/hr to with 12 decimal places.

    Those speeds are simply to low for relativistic effects to be measurable.
     
  4. Jan 17, 2009 #3
    3.33 m/s [for stationary observer in ground]
     
  5. Jan 17, 2009 #4

    Fredrik

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    Microsoft PowerToy Calculator for Windows XP says 11.999999999999999258233295964254424402093624772443805600625656194569150201085437567008465314216160709462212415964961122075175062 :smile:

    By the way, that has to be the slowest runner ever, considering that normal walking speed is about 6 km/h. :wink:
     
  6. Jan 17, 2009 #5

    HallsofIvy

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    Hey, YOU try running on top of a moving train!
     
  7. Jan 20, 2009 #6
    You're at rest. You are always at rest relative to yourself.
     
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