# Machine Kinematics Questions and Answers – Friction in Journal Bearing- Friction Circle

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This set of Machine Kinematics Multiple Choice Questions & Answers (MCQs) focuses on “Friction in Journal Bearing- Friction Circle”.

1. The minimum force required to slide a body of weight W on a rough horizontal plane is
a) W sinϴ
b) W cosϴ
c) W tanϴ
d) W cosecϴ

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).

2. A body will begin to move down an inclined plane, if the angle of inclination of the plane is ____________ the angle of friction.
a) equal to
b) less than
c) greater than
d) none of the mentioned

Explanation: None.

3. 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
a) P = W tanα
b) P = W tan (α + ɸ)
c) P = W (sinα + μ cosα)
d) 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).
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4. The coefficient of friction is the ratio of the limiting friction to the normal reaction between the two bodies.
a) True
b) 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,
μ = F/RN.

5. In a screw jack, the effort required to lift the load W is given by
a) P = W tan (α – ɸ)
b) P = W tan (α + ɸ)
c) P = W tan (ɸ – α)
d) P = W cos (α + ɸ)

Explanation: The effort required at the circumference of the screw to lift the load W is given by
P = W tan (α + ɸ)
The effort required at the circumference of the screw to lower the load W is given by
P = W tan (ɸ – α).

6. In a screw jack, the effort required to lower the load W is given by
a) P = W tan (α – ɸ)
b) P = W tan (α + ɸ)
c) P = W tan (ɸ – α)
d) P = W cos (α + ɸ)

Explanation: The effort required at the circumference of the screw to lower the load W is given by
P = W tan (ɸ – α)
The effort required at the circumference of the screw to lift the load W is given by
P = W tan (α + ɸ).

7. The frictional torque for square thread at the mean radius r while raising load W is given by
a) T = W.rtan(α – ɸ)
b) T = W.rtan(α + ɸ)
c) T = W.rtanα
d) T = W.rtanɸ

Explanation: None.

8. Efficiency of a screw jack is given by
a) tan(α + ɸ)/tanα
b) tanα/ tan(α + ɸ)
c) tan(α – ɸ)/tanα
d) tanα/tan(α – ɸ)

Explanation: None.

9. The load cup of a screw jack is made separate from the head of the spindle to
a) enhance the load carrying capacity of the jack
b) reduce the effort needed for lifting the working load
c) reduce the value of frictional torque required to be countered for lifting the load
d) 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.

10. The efficiency of the a screw jack is maximum, when
a) α = 450 + ɸ/2
b) α = 450 – ɸ/2
c) α = 900 + ɸ
d) α = 900 – ɸ

Explanation: None.

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