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 30.0 g and electrical resistance 0.400 ? rests on parallel horizontal rails that have negligible electric resistance. the rails are a distance l = 9.00 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 = 0.131 t . assume that the rod has a slightly flattened bottom so that it slides instead of rolling. use 9.80 m/s2 for the magnitude of the acceleration due to gravity. find the coefficient of static friction between the rod and the rails.