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
All of these
Is independent of the area of contact, between the two surfaces

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Engineering Mechanics
The Cartesian equation of trajectory is (where u = Velocity of projection, α = Angle of projection, and x, y = Co-ordinates of any point on the trajectory after t seconds.)

y = x. tanα - (gx²/2u² cos²α)
y = (gx²/2u² cos²α) - x. tanα
y = (gx²/2u² cos²α) + x. tanα
y = x. tanα + (gx²/2u² cos²α)

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

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