Machine Kinematics

Friction in Journal Bearing- Friction Circle

Question 1
Marks : +2 | -2
Pass Ratio : 100%
In a screw jack, the effort required to lift the load W is given by
P = W tan (α – ɸ)
P = W tan (α + ɸ)
P = W tan (ɸ – α)
P = W cos (α + ɸ)
Explanation:
The effort required at the circumference of the screw to lift the load W is given by
Question 2
Marks : +2 | -2
Pass Ratio : 100%
Efficiency of a screw jack is given by
tan(α + ɸ)/tanα
tanα/ tan(α + ɸ)
tan(α – ɸ)/tanα
tanα/tan(α – ɸ)
Explanation:
None.
Question 3
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Pass Ratio : 100%
The load cup of a screw jack is made separate from the head of the spindle to
enhance the load carrying capacity of the jack
reduce the effort needed for lifting the working load
reduce the value of frictional torque required to be countered for lifting the load
prevent the rotation of load being lifted
Explanation:
In screw jack, the load to be raised or lowered, is placed on the head of the square threaded rod which is rotated by the application of an effort at the end of the lever for lifting or lowering the load.
Question 4
Marks : +2 | -2
Pass Ratio : 100%
The minimum force required to slide a body of weight W on a rough horizontal plane is
W sinÏ´
W cosÏ´
W tanÏ´
W cosecÏ´
Explanation:
The minimum force required to slide a body of weight W on a rough horizontal plane is W sinϴ. A body of weight W is required to move up the rough inclined plane whose angle of inclination with the horizontal is α. The effort applied parallel to the plane is given by P = W (sinα + μ cosα).
Question 5
Marks : +2 | -2
Pass Ratio : 100%
The coefficient of friction is the ratio of the limiting friction to the normal reaction between the two bodies.
True
False
Explanation:
The coefficient of friction is defined as the ratio of the limiting friction(F) to the normal reaction(RN) between the two bodies. Mathematically,
Question 6
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A body will begin to move down an inclined plane, if the angle of inclination of the plane is ____________ the angle of friction.
equal to
less than
greater than
none of the mentioned
Explanation:
None.
Question 7
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Pass Ratio : 100%
The frictional torque for square thread at the mean radius r while raising load W is given by
T = W.rtan(α – ɸ)
T = W.rtan(α + ɸ)
T = W.rtanα
T = W.rtanɸ
Explanation:
None.
Question 8
Marks : +2 | -2
Pass Ratio : 100%
In a screw jack, the effort required to lower the load W is given by
P = W tan (α – ɸ)
P = W tan (α + ɸ)
P = W tan (ɸ – α)
P = W cos (α + ɸ)
Explanation:
The effort required at the circumference of the screw to lower the load W is given by
Question 9
Marks : +2 | -2
Pass Ratio : 100%
The efficiency of the a screw jack is maximum, when
α = 450 + ɸ/2
α = 450 – ɸ/2
α = 900 + ɸ
α = 900 – ɸ
Explanation:
None.
Question 10
Marks : +2 | -2
Pass Ratio : 100%
A body of weight W is required to move up the rough inclined plane whose angle of inclination with the horizontal is α. The effort applied parallel to the plane is given by
P = W tanα
P = W tan (α + ɸ)
P = W (sinα + μ cosα)
P = W (cosα + μ sinα)
Explanation:
The minimum force required to slide a body of weight W on a rough horizontal plane is W sinϴ. A body of weight W is required to move up the rough inclined plane whose angle of inclination with the horizontal is α. The effort applied parallel to the plane is given by P = W (sinα + μ cosα).