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

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Engineering Mechanics
The static friction

Bears a constant ratio to the normal reaction between the two surfaces
Always acts in a direction, opposite to that in which the body tends to move
Is independent of the area of contact, between the two surfaces
All of these

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