Rail gun... please help?

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 m 30.0 g and electrical resistance 0.300 \Omega rests on parallel horizontal rails that have negligible electric resistance. The rails are a distance L = 7.00 cm apart. 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 = 0.126 T. ume 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_s, the coefficient of static friction between the rod and the rails.