college algebra

The electrical resistance of a wire of a given material varies as its length and inversely as the square of the diameter. if a wire 300 feet long and 0.05 inches in diameter has a resistance of 30 ohms, (a) find the resistance of a wire which is 1000 feet long and 0.02 inch in diameter (b) find the length of a wire whose resistance is 20 ohms and diameter is 0.03 inch

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asked by Sam
  1. R = k L/d^2
    given case: L = 300, d = .05, R = 30
    30 = k (300/.05^2)
    k = .0025(30)/300 = .00025

    R = .00025 L/d^2

    a) plug in the given values to find R

    b) plugging in our values:
    20 = .00025 L/.03^2
    L = .0009(20)/.00025 = 72
    the wire is 72 inches long

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    posted by Reiny

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