A body placed on a rough inclined plane just begins to slide

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#1

A body placed on a rough inclined plane just begins to slide, when the slope of the plane equal to 1 in 4. Calculate the coefficient of friction.


#2

The slope of the plane equal to 1 in 4 implies that if BC = 1 and AB = 4. Suppose that the plane is inclined at angle $\theta$ with the horizontal AC. From the relation between the coefficient of friction and angle of repose, we have