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
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
Which is correct statement? Stress concentration in static loading is

Equally serious in both types of materials
Very serious in brittle materials and less serious in ductile materials
Very serious in ductile materials and less serious in brittle materials
Seriousness would depend on other factors

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