A rail gun uses electromagnetic forces to accelerate a projectile to very high v

Question

A rail gun uses electromagnetic forces to accelerate a projectile to very high velocities. The basic mechanism of acceleration is relatively simple and can be illustrated in the following example. A metal rod of mass 50.0 g and electrical resistance 0.200 Ohm rests on parallel horizontal rails that have negligible electric resistance. The rails are a distance L = 8.00 cm apart. (Figure 1) The rails are also connected to a voltage source providing a voltage of V = 5.00 V. The rod is placed in a vertical magnetic field. The rod begins to slide when the field reaches the value B = 0.123 T. Assume that the rod has a slightly flattened bottom so that it slides instead of rolling. Use 9.80 m/s^2 for the magnitude of the acceleration due to gravity. Find mu_g, the coefficient of static friction between the rod and the rails. Give your answer numerically.

Explanation / Answer

current = Voltage/resistance = 5V /0.200 = 25A.

q*v=I*L =25*0.08=2coulomb*m/s

F = q*v x B 2*0.123=0.246N

Normal Force=mg 0.05*9.81=0.4905N

coefficient of static friction=0.246/0.4905=0.50

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