Engineering Mechanics
Which of the following statement is incorrect?

A force acting in the opposite direction to the motion of the body is called force of friction
The velocity ratio of a machine is the ratio of load lifted to the effort applied
The ratio of the limiting friction to the normal reaction is called coefficient of friction
A machine whose efficiency is 100% is known as an ideal machine

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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

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

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Engineering Mechanics
According to the law of moments, if a number of coplanar forces acting on a particle are in equilibrium, then

The algebraic sum of their moments about any point is equal to the moment of their resultant force about the same point
The algebraic sum of their moments about any point in their plane is zero
Their algebraic sum is zero
Their lines of action are at equal distances

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