3/10/2014 Master Ithttp://www.webassign.net/v4cgi/questions/tutorial_popup.tpl 1/2Master ItThe figure below shows a top view of a bar that can slide on two frictionless rails. The resistor is and a 2.50T magnetic field is directed perpendicularly downward, into the page. Let = 1.20m.(a) Calculate the applied force required to move the bar to the right at a constant speed of 2.40 m/s.(b) At what rate is energy delivered to the resistor?Part 1 of 4 ConceptualizeThe motion of the bar induces an emf in the rectangle. The emf produces a current in the circuit, includingthe bar. Then the magnetic field exerts a force on the bar, and an outside agent must counterbalance thisforce to keep the bar moving at constant speed.Part 2 of 4 CategorizeWe will use the rigid body in equilibrium model together with the definition of resistance and Faraday's law.Part 3 of 4 Analyze(a) At constant speed, the net force on the moving bar is zero. For the applied force, we havewhere the current in the bar is and the motional emf is Therefore, the magnitude of theapplied force necessary to keep the bar moving to the right at constant speed v is given byPart 4 of 4 Analyze(b) The outside agent pulling the bar must provide input power given byR = 5.30 Ω,app = I( × ),F L BI = /R = B v.Fapp = B = = = 4.08 N.B vRB2 2vR 2.5 T 1.2 m 2.4 m/s 5.3 Ω2 2 3/10/2014 Master Ithttp://www.webassign.net/v4cgi/questions/tutorial_popup.tpl 2/2FinalizeIn terms of energy, the circuit is a nonisolated system in steady state. The energy delivered to the circuit bywork done by the applied force is delivered to the resistor by electrical transmission. The energy can leavethe resistor as energy transferred by heat into the surrounding air. The circuit in this problem is electricallysimple. Unlike a circuit connected to a battery whose chemical reaction and loss of chemical energy wewould have considered, in this circuit we can account completely for the energy transmission. We could alsocompute power as P = Fappv = 4.08 N 2.4 m/s = 9.78
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