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

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%
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

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

When the maximum shear stress in a biaxial stress system reaches the shear stress at elastic limit 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 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
When the maximum principal stress in a biaxial stress system reaches the elastic limit of the material in a simple tension test

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