A bar magnet is released from rest and falls through a very long vertical copper tube. If a represents the acceleration of the magnet and v represents its downward velocity, which of the following best describes the graph of acceleration a (on the y-axis) versus velocity v (on the x-axis) before it reaches terminal velocity?

Step-by-step solution

As the magnet falls through the copper tube, the changing magnetic flux induces eddy currents in the tube. According to Faraday's law of induction, the induced electromotive force (EMF) is directly proportional to the velocity of the magnet v . The induced eddy currents are I = EMF R , which means I v . By Lenz's law, these currents produce an upward magnetic drag force F_ drag that opposes the motion. Since the magnetic force is proportional to the induced current, F_ drag v . We can write F_ drag = kv , where k i