Applied Mechanics and Graphic Statics
On a ladder resting on a rough ground and leaning against a smooth vertical wall, the force of friction acts

Downwards at its upper end
Zero at its upper end
Upwards at its upper end
Perpendicular to the wall at its upper end

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Applied Mechanics and Graphic Statics
If a set of given forces are such that their free vectors build a closed polygon, then

The resultant force is zero but resultant couple may not be zero
The resultant force and resultant couple both may not be zero
The resultant force is zero but resultant couple is not zero
The resultant force and resultant couple are always zero

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Applied Mechanics and Graphic Statics
The resolved part of the resultant of two forces inclined at an angle θ in a given direction is

Arithmetical sum of the resolved parts of the forces in the direction
Sum of the forces multiplied by the tangent θ°
Difference of the forces multiplied by cosine θ°
Algebraic sum of the resolved parts of the forces in the direction

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