Machine Design
When a hole of diameter ‘d’ is punched in a metal of thickness 't', then the force required to punch a hole is equal to (where τu = Ultimate shear strength of the material of the plate)

π/4 × d² × tτu
π/4 × d².τu
πd.t.τu
t.τu

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Machine Design
Which of the following statement is correct regarding power screws?

The efficiency of a self locking screw can not be more than 50%
The efficiency of Acme (trapezoidal) thread is less than that of a square thread
If the friction angle is less than the helix angle of the screw, then the efficiency will be more than 50%
Both (A) and (B)

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Machine Design
The face of the tooth is the

Surface of the top of the tooth
Surface of the tooth below the pitch surface
Surface of the tooth above the pitch surface
Width of the tooth measured along the pitch circle

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