WEBVTT

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Here is the problem: A crate presses on the floor with a normal force of 55 N. If μ equals 0.4, what is the friction force?

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Use the friction formula, rearranged for the unknown, in SI units.

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Formula: friction.

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Substitute the known values.

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So the answer is friction force f equals 22 N.

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Kinetic friction opposes sliding with magnitude f equals μₖN; static friction can take any value up to μₛN. On a level surface with no other vertical forces, the normal force equals the weight mg.

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Substituted every value back into the formula: both sides agree, which checks out.