Rail Run A rail gun uses electromagnetic forces to accelerate a projectile to ve

Question

Rail Run

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 0.500? rests on parallel horizontal rails that have negligible electric resistance. The rails are a distance L = 10.0cm 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/s2for the magnitude of the acceleration due to gravity.

Part A

Find ?s, the coefficient of static friction between the rod and the rails.

Rail Run 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 0.500? rests on parallel horizontal rails that have negligible electric resistance. The rails are a distance L = 10.0cm 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/s2for the magnitude of the acceleration due to gravity. Part A Find ?s, the coefficient of static friction between the rod and the rails.

Explanation / Answer

Force on the rod =frictional force

BIL =usmg

since current

I=V/R

=>BLV/R =usmg

So coefficient of static friction between the rod and the rails is

us=BLV/mgR =0.196*0.1*5/(40*10-3)*9.8*0.5

us=0.5

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