A 20-pound box sits at rest on a horizontal surface, and there is friction between the box and the surface. One side of the surface is raised slowly to create a ramp. The friction force f opposes the direction of motion and is proportional to the normal force F_N exerted by the surface on the box. The proportionality constant is called the coefficient of friction, μ. When the angle of the ramp,θ, reaches 20°, the box begins to slide. Find the value of μ to two decimal places.

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f FN 20 pounds 0