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 40.0g and electrical resistance 0.300? rests on parallel horizontal rails that have negligible electric resistance. The rails are a distance L = 6.00cm apart. (Figure 1) The rails are also connected to a voltage source providing a voltage of V = 5.00V. The rod is placed in a vertical magnetic field. The rod begins to slide when the field reaches the value B = 0.196T. Assume that the rod has a slightly flattened bottom so that it slides instead of rolling. Use 9.80m/s2 for the magnitude of the acceleration due to gravity. Find ?s, the coefficient of static friction between the rodand the rails.

Explanation / Answer

I = V/R = 5/0.3 = 16.67 A

F magnetic = I L B

to start moving Fmagnetic = Ffriction

I L B = u m g

16.67*6.0E-3*0.196 = u*40.0E-3*9.8

u=0.05

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