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Homework Help: Currents and motional emf

  1. Aug 3, 2009 #1
    1. A 50 g horizontal metal bar, 12 cm long, is free to slide up and down between two tall, vertical metal rods. A 0.060 T magnetic field is directed perpendicular to the plane of the rods. The bar is raised to near the top of the rods, and a 1.0 Ohm resistor is connected across the two rods at the top. Then the bar is dropped. What is the terminal speed at which the bar falls? Ignore air resistance.

    2. I= ε/R= (vlB)/R

    I is current, ε is motional emf, R is resistance, v is velocity, l is length, B is magnetic field.

    3. I don't even know where to start. I know that R= 1.0, l= .12 m, B= 0.060 T. What do I do with the 50 g?
  2. jcsd
  3. Aug 3, 2009 #2


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    I will start you off by asking and answering the first question. You have to answer the rest to get going.

    Q0. What does "terminal velocity" mean?
    Ans. That the velocity reaches a final value that stays the same.

    Q1. If the velocity stays the same what is the value of the acceleration?
    Q2. If the acceleration has that value what does that say about the net force on the bar?
    Q3. How many forces act on the bar when it reaches terminal velocity?
    Q4. Given all your previous answers, what is the relation linking the forces acting on the bar?
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