# Projectile Launcher, large current, closed loop, magnetic field

1. Apr 17, 2010

### thermocleanse

1. The problem statement, all variables and given/known data
A projecticle launcher is shown in the attachment. A large current moves in a closed loop composed of fixed rails, a power supply, and a very light, almost frictionless bar touching the rails. A magnetic field is perpendicular to the plane of the circuit. If the bar has a length L=0.22 m and a mass of 0.0015 kg and is placed n a field of 1.7 T, what constant current flow is needed to accelerate the bar from rest to 28 m/s in a distance of 1.0 m? In what direction must the magnetic field point?

2. Relevant equations
F=ma
F=ILB

3. The attempt at a solution
I'm having a hard time conceptualizing this problem and would like any assistance. Thank you.

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2. Apr 18, 2010

### AtticusFinch

Current is simply protons moving in one direction. Moving charges in a magnetic field experience a force. Consequently the bar experiences a force. You've basically solved 90% of the problem with the two equations you wrote down.

BIL = ma

You can easily use the information given and kinematics to figure out the acceleration. Then just solve for I.

Use the right-hand rule for the second question.