A sort of €˜€™projectile launcher€™€™ is shown in Fig. 20-65. 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 mar has a length L = 22cm, a mass of 1.5g, and is placed in a field of 1.7T, what constant current flow is needed to accelerate the bar from rest to 28m/s in a distance of 1.0m? in what must the magnetic field point?

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