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Homework Help: Lorentz Transformation

  1. Nov 24, 2008 #1
    1. The problem statement, all variables and given/known data

    An electron with rest mass m0 = 9.11E10-31 kg and charge e= 1.6E10-19 C was accelerated with an acceleration voltage U=30 kV

    a) What is its velocity , momentum and energy in a classical picture ?
    b)What is its velocity , momentum and energy in a relativistic picture ? What is its relativistic mass ?

    c) If the acceleration voltage was only U=30 V , What is the electron's velocity , momentum and energy ? Would you use the classical or the relativistic picture and why ?

    2. Relevant equations

    For Part a) v = dx / dt
    p = mv
    energy = (1/2) m0 * v2

    For Part b) Lorentz Transformation for Velocity
    ux' = [ux - v] / [ 1+ (vux /c^2) ]
    Where ux' as i understand is the velocity , moving frame of reference .

    Relativisitc momentum
    p= m0 * u / ((1-(u^2/c^2))^1/2

    Relativistic Energy

    Relativisitic mass
    mr = m0 / ((1-(u^2/c^2))^1/2

    3. The attempt at a solution

    If the above equations are correct in this case so

    For part a) for velocity i m not getting how can i calculate the numerical figure
    for momentum offcourse if i have velocity i can simply put it in the equation
    for energy as well i need velcocity

    For part b)

    for velocity what is the difference in Ux and V ?
    What U i have to substitute for relativistic momentum ?
    For Energy :
    mass = 9.11 E 10 -31
    For Relativistic mass
    m0 = 9.11 E 10 -31

    Thanks in advance
  2. jcsd
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