Arail 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 0.300 \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 = 0.210 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_s, the coefficient of static friction between the rod and the rails.