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 and resultant couple are always zero
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

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Applied Mechanics and Graphic Statics
One end of an elastic string of natural length ‘l’ and modulus ‘X’ is kept fixed while to the other end is attached a particle of mass m which is hanging freely under gravity. The particle is pulled down vertically through a distance ‘x’, held at rest and then released.The motion is

A simple harmonic motion
A damped oscillatory motion
A rectilinear motion with constant speed
None of these

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