In Figure force F is applied to a crate of mass m on a floor where the coefficient of static friction between crate and floor is ?s. Angle ? is initially 0o but is gradually increased so that the force vector rotates clockwise in the figure. During the rotation, the magnitude F of the force is continuously adjusted so that the crate is always on the verge of sliding. For ?s = 0.70,(a) Plot the ratio F/mg versus g and(b) Determine the angle ? inf at which the ratio approaches an infinite value.(c) Does lubricating the floor increase or decrease ? inf, or is the value unchanged?(d) What is ? inf for ?s = 0.60?

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