Engineering Mechanics
Angle of friction is the

The ratio of minimum friction force to the friction force acting when the body is just about to move
Angle between normal reaction and the resultant of normal reaction and the limiting friction
The ratio of minimum friction force to friction force acting when the body is in motion
Ratio of limiting friction and normal reaction

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Engineering Mechanics
A semicircular disc rests on a horizontal surface with its top flat surface horizontal and circular portion touching down. The coefficient of friction between semi circular disc and horizontal surface is µ. This disc is to be pulled by a horizontal force applied at one edge and it always remains horizontal. When the disc is about to start moving, its top horizontal force will

Slant down towards direction of pull
Remain horizontal
Slant up towards direction of pull
None of these

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