Challenge date 06-01-2026

See the figure below. Planar analysis. A half-disk (semicircular shape, uniform mass density) rests on a rigid horizontal plane with Coulomb friction coefficient µ. A force F acts on the right corner as shown, making a constant angle β = 20◦ with horizontal. The disk rolls to the right and is at equilibrium. The force F is slowly increased, maintaining equilibrium, until the roll angle is θ = 30◦. At this configuration, the system is at impending slip. Find µ to 3 significant digits.

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Figure for Challenge 06-01-2025