<p>#65 in college physics 8th edition (additional problems)<br /><br />A rolling

Question

<p>#65 in college physics 8th edition (additional problems)<br /><br />A rolling axle, 1.50 m long, is pushed along horizontal rails at a constant speed v= 3.00 m/s. A resistor R = 0.400&#160;&#937; is connected to the rails at points a and b, directly opposite each other. (The wheels make good electrical contact with the rails, so the axle, rails, and R form a closed-loop circuit. The only significant resistance in the circuit is R.) A uniform magnetic field B = 0.800 T is directed vertically downward.</p>
<p>(a). Find the induced current I in the resistor. <br />(b). What horizontal force F is required to keep the axle rolling at constant speed?</p>
<p>(c). Which end of the resistor, a or b, is at the higher electric potential? <br />(d). After the axle rolls past the resistor, does the current in R reverse direction?<br /><br /></p>

Explanation / Answer

The speed of rail, v = 3 m/s The resistor, R = 0.4 The magnetic field, B = 0.8 T The length of the axle, l = 1.5 m a) Induced emf is given by the formula, E = Blv The above equation can be written as, IR = Blv And from the above, I = Blv/R = 0.8*1.5*3 / 0.4 = 9 A b) The force is given by the formula, F = Bil = 0.8 * 9 * 1.5 = 10.8 N I have no idea about the options (c) and (d) thanks

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