Engineering Mechanics
Which is the correct statement about law of polygon of forces?

If a polygon representing forces acting at a point is closed then forces are in equilibrium
If any number of forces acting at a point can be represented in direction and magnitude by the sides of a polygon, then the forces are in equilibrium
If any number of forces acting at a point can be represented in direction and magnitude by the sides of a polygon taken in order, then the forces are in equilibrium
If any number of forces acting at a point can be represented by the sides of a polygon taken in order, then the forces are in equilibrium

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Engineering Mechanics
According to Newton's first law of motion,

The rate of change of momentum is directly proportional to the impressed force, and takes place in the same direction, in which the force acts
To every action, there is always an equal and opposite reaction
None of these
Everybody continues in its state of rest or of uniform motion, in a straight line, unless it is acted upon by some external force

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Engineering Mechanics
The loss of kinetic energy during inelastic impact, is given by (where m1 = Mass of the first body,m2 = Mass of the second body, and u1 and u2 = Velocities of the first and second bodies respectively.)

[2(m₁ + m₂)/m₁ m₂] (u₁² - u₂²)
[m₁ m₂/2(m₁ + m₂)] (u₁ - u₂)²
[2(m₁ + m₂)/m₁ m₂] (u₁ - u₂)²
[m₁ m₂/2(m₁ + m₂)] (u₁² - u₂²)

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