Machine Design
The velocity factor for very accurately cut and ground metallic gears operating at velocities upto __________ are equal to 6/(6 + v).

20 m/s
12.5 m/s
15 m/s
10 m/s

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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
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%

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Machine Design
Jam nut is a locking device in which

A hard fibre or nylon cotter is recessed in the nut and becomes threaded as the nut is screwed on the bolt causing a tight grip
Through slots are made at top and a cotter pin is passed through these and a hole in the bolt, and cotter spitted and bent in reverse direction at other end
A slot is cut partly in middle of nut and then slot reduced by tightening a screw
One smaller nut is tightened over main nut and main nut tightened against smaller one by loosening, creating friction jamming

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Machine Design
In hydrostatic bearings

The Oil film pressure is generated only by the rotation of the journal
The oil film is maintained by supplying oil under pressure
Do not require external supply of lubricant
Grease is used for lubrication

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