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Homework Help: Terminal Speed expression

  1. May 30, 2014 #1
    1. The problem statement, all variables and given/known data

    2. Relevant equations
    That is the solution:

    3. The attempt at a solution
    I think ε≠Bvl because ε = - dø/dt=- Bd(v.t)/dt, v is not constant.
    Why ε=Bvl???
  2. jcsd
  3. May 30, 2014 #2


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    Gold Member

    The induced emf in the loop is related to the change in flux through a surface whose boundary is the loop: $$\epsilon = -\frac{\text{d} \phi}{\text{d}t} = -\frac{\text{d}}{\text{d}t} \int_S \mathbf{B} \cdot \mathbf{dS}$$
    In your case, the B field is of constant magnitude and direction and dS instantaneously is Ldx.
  4. May 30, 2014 #3
    dø/dt = d(B. Area)/dt = d(BLx)/dt = BL dx/dt = BLv.
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