Magnetic Induction Through a Moving Wire

AI Thread Summary
A u-shaped conducting wire in a constant magnetic field of 0.9 tesla allows a 7 m rod to slide down, generating an electromotive force (emf) and current. The magnetic force counteracts gravity, leading to a maximum velocity when the forces balance. The calculated gravitational force acting on the rod is 49 N, which is crucial for determining the current and velocity. Using the equations for emf and current, the maximum velocity of the rod is found to be 1.97 m/s with a current of 1.56 A. The calculations confirm that the forces acting on the rod are correctly accounted for in the solution.
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Homework Statement


A very long u-shape conducting wire is placed vertically in a constant magnetic field. The magnetic field is perpendicular to the plane of the wire. The strength of the magnetic field is B = 0.9 tesla. A conducting rod is placed on the wire, as shown in the picture. The length of the rod is 7 m. The rod has a mass of 5 kg and a resistance of 8 Ohm. When the rod is released from rest, it start to slide down but maintain good contact with the u-shape wire. After some time, the rod reaches a maximum velocity and moves constantly thereafter. You can ignore the resistance of the u-shape wire and the friction between the rod and the wire.
B = 0.9T ; L = 7m ; R = 8Ω ; g= 9.8m/s
What is the maximum velocity of the moving rod?
What is the current in the loop when the moving rod reaches maximum velocity?

Homework Equations


ε= v*L*B
I=(v*L*B)/R
F = I*L*B

or
F = (v(L*B)^2)/R


The Attempt at a Solution



Ok I know that once this wire begins to move it creates an emf and a current. The magnetic force generated is going to counteract my force of gravity. My assumption is that when it reaches its maximum velocity the F will be 9.8 as well since it can no longer change.
So:
F = 9.8N?
I've tried plugging in from here and have not been able to get a correct answer, where am I going wrong?
9.8 = I(7)(0.9) thus I = 1.56A

1.56 = (v(7)(0.9))/8 thus v = 1.97m/s
 

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As soon as I posted this I remembered that the F is ACTING on MASS. This makes my F = 49N
D'oh!
I'll leave this here I guess.
Plugging in it all worked out smoothly :)
 
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