4 Friction (wedge Friction) 3l3e59

FRICTION (WEDGE FRICTION)

MAIT

Q. 1: Explain how a wedge is used for raising heavy loads. Also gives principle. Solution: Principle of wedge : A wedge is small piece of material with two of their opposite faces not parallel. To lift a block of weight W,, it is pushed by a horizontal force P which lifts the block by imparting a reaction on the block in a direction 1r to meeting surface which is always greater than the total downward force applied by block W This will cause a resultant force acting in a upward direction on block and it moves up.

Q. 2: Two wedge blocks A and B are employed to raise a load of 2000 N resting on another block C by the application of force P as shown in Fig. 9.66. Neglecting weights of the wedge blocks and assuming co-efficient co of friction µ = 0.25 for all the surfaces, determine the value of P for impending upward motion of the block C. Solution: The block C,, under the action of forces P on blocks A and B, tends to move upward. Hence the frictional forces will act downward. What holds good for block A, the same will hold good for block B tan ϕ = µ = 0.25 (given), where ϕ is the angle of friction ϕ = 14° Refer Fig. 1

Consider the equilibrium of block C:: Refer Fig.2 It is acted upon by the following forces:: (i) Load 2000 N, (ii) Total reaction RA offered by wedge block A, and (iii) Total reaction RB offered by wedge block B. Using Lami's theorem, we get

Refer following Fig. 4:

Compiled by: RAMAKANT RANA “[email protected]”

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FRICTION (WEDGE FRICTION)

MAIT

Consider equilibrium of block A: It is acted upon by the following forces:: (i) Force P, (ii) RA (from block C), and (iii) Total reaction R offered by horizontal surface. Using Lami’s theorem, we have

Hence P = 803 N .......ANS

Compiled by: RAMAKANT RANA “[email protected]”

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