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

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

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Machine Design
According to Rankine's theory, the failure occurs at a point in a member

When the maximum principal stress in a biaxial stress system reaches the elastic limit of the material in a simple tension test
When the maximum principal strain in a biaxial stress system reaches the strain at the elastic limit as determined from a simple tension test
When the maximum shear stress in a biaxial stress system reaches the shear stress at elastic limit in a simple tension test
When the strain energy per unit volume in a biaxial stress system reaches the strain energy at the elastic limit per unit volume as determined from a simple tension test

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