Download A rail gun uses electromagnetic forces to accelerate a projectile to

Rail Gun
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 0.100 Ω rests on parallel horizontal rails that
have negligible electric resistance. The rails are a distance L = 10.0 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 = 4.90×10−2 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 μs, the coefficient of static friction between the rod and the rails?
Current carrying conductor experiences a magnetic force in horizontal direction as B is in zdirection and current flow is in y-direction. Conductor slides when B becomes 4.9*10-2 T. This
should be equal to frictional force. Hence, we should have
s mg  BIL  s 
5
V
 0.1
 L 4.9 102 
0.1
R

 0.5 . Ans.
50
mg
 9.8
1000
B