Power in circuits:

$\overline{){\mathbf{P}}{\mathbf{=}}{\mathbf{V}}{\mathbf{i}}{\mathbf{=}}{{\mathbf{i}}}^{{\mathbf{2}}}{\mathbf{R}}{\mathbf{=}}\frac{{\mathbf{V}}^{\mathbf{2}}}{\mathbf{R}}}$

Also,

$\overline{){\mathbf{P}}{\mathbf{=}}{\mathbf{F}}{\mathbf{v}}}$

Force:

$\overline{){\mathbf{F}}{\mathbf{=}}{\mathbf{i}}{\mathbf{L}}{\mathbf{B}}}$

Given that 3.9 W of power is to be dissipated, we'll consider the equation:

P = V^{2}/R

V = sqrt(PR) = sqrt[(3.9)(0.33)] = 1.134V

A 9.0-cm-long wire is pulled along a U-shaped conducting rail in a perpendicular magnetic field. The total resistance of the wire and rail is 0.33 Ohms. Pulling the wire with a force of 1.2 N causes 3.9 W of power to be dissipated in the circuit. What is the speed of the wire when pulled with 1.2 N?

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