This set of Engineering Mechanics Multiple Choice Questions & Answers (MCQs) focuses on “Frictional Forces on Journal Bearings”.

1. The journal bearings are generally used in __________

a) Belts

b) Columns

c) Beams

d) Supports

View Answer

Explanation: The journal bearings are being used in the supports. They are used as to support the loadings. This means that the more the bearings the more is the stable the structure. Thus the use of journal bearings.

2. At what conditions does the Coulomb friction occur between the surfaces in contact of journal bearing?

a) When there is no lubricating fluid

b) When there is no friction fluid

c) When there is no adhesive fluid

d) When there is no cohesive fluid

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Explanation: When there is no lubricating fluid present between the surfaces in contact, the dry friction occurs. Thus as the name suggests dry friction. When there is no liquid present over there the surfaces are going to be said dry only. Thus the term dry friction.

3. Determine the moment about the point Q by the force shown as 400N.

a) -98.6kN

b) 98.6kN

c) -98.6iN

d) -98.6jN

View Answer

Explanation: As we know that the moment is the cross product of the force and the distance between the point of contact of the force and the point about which moment needs to be calculated. Thus forming the distance vector and then crossing it with the force will give us the answer. Remember force also needs to be in the vector form for doing the cross product.

4. We first make equilibrium equations of the sections involving the journal bearings by considering all the three dimensional forces acting on the section chosen and then the free body diagram is made and solved.

a) The first part of the statement is false and other part is true

b) The first part of the statement is false and other part is false too

c) The first part of the statement is true and other part is false

d) The first part of the statement is true and other part is true too

View Answer

Explanation: We first make the free body diagram of journal bearings and then we make the equilibrium equations to satisfy the given conditions. This helps us to solve the question easily. As this reduces the part of imagination and increases accuracy too.

5. To know the rotations involved in the journal bearings we use right handed coordinate system, in that system which of the following is followed (consider the mentioned axis to be positive)?

a) Thumb is z-axis, fingers curled from x-axis to y-axis

b) Thumb is x-axis, fingers curled from z-axis to y-axis

c) Thumb is y-axis, fingers curled from x-axis to z-axis

d) Thumb is z-axis, fingers curled from y-axis to x-axis

View Answer

Explanation: As right handed coordinate system means that you are curling your fingers from positive x-axis towards y-axis and the thumb which is projected is pointed to the positive z-axis. Thus visualizing the same and knowing the basic members of the axis will not create many problems.

6. The moment is the cross product of which two vectors in the calculations of the journal bearings?

a) Force and Radius vectors

b) Radius and Force vectors

c) Force and Radius scalars

d) Radius and Force scalars

View Answer

Explanation: The cross product needs to take in the proper sequence. If not taken then the answer is just the opposite of the true answer. That’s why, the answer is not the Force and Radius vectors, but the Radius and Force vectors. Because the moment has its direction, as many of the cross products have, and thus precaution needs to be taken.

7. The basic type of motion of a body is not the translation motion only.

a) True

b) False

View Answer

Explanation: The basic types of the motion of the body are translation and rotational. In which translation means the motion is a straight motion while the in the rotational motion the body is moving of the body along the axis. The pivots do a circular motion.

8. Determine the moment about the point P.

a) 460Nm

b) 500Nm

c) 705Nm

d) 0Nm

View Answer

Explanation: As we know that the moment is the cross product of the force and the distance between the point of contact of the force and the point about which moment needs to be calculated. Thus forming the distance vector and then crossing it with the force will give us the answer. Remember force also needs to be in the vector form for doing the cross product.

9. Sometime the principle of transmissibility is somehow applied to journal bearings. It states that:

a) It states that the force acting on the body is a sliding vector

b) It states that the force acting on the body is a rolling vector

c) It states that the force acting on the body is a wedging vector

d) It states that the force acting on the body is a unit vector

View Answer

Explanation: Principle of transmissibility states that the force acting on the body is a sliding vector. That is it can be applied at any point of the body. It will give the same effect as if applied at any point other that the specific point. Thus the answer.

10. Coplanar forces are not easily simplified in the simplification of the force and couple system in the calculations of forces in the journal bearings.

a) True

b) False

View Answer

Explanation: The coplanar forces can be easily simplified in the simplification of the force and couple system. This is not only for the coplanar system of the forces but for any of the dimension vector. Which means the answer is false.

11. There are some of the applications of the two force and three force members in the journal bearings. The difference between the two and the three force members is:

a) The former is collinear and the latter is parallel

b) The former is parallel and the latter is perpendicular

c) The former is perpendicular and the latter is collinear

d) The former is acting on two points in the body while the latter is on three points

View Answer

Explanation: The definition of the two force member only defines that the forces are being acted on the two points on the body. So does is the definition of the three forces members. The points of action of the three forces are three.

12. Which of the following is true for the determination of the rotational effect of the bearings?

a) If we are considering the clockwise direction to be positive then the rotation along the counter clockwise direction is negative

b) If we are considering the clockwise direction to be negative then the rotation along the counter clockwise direction is also negative as no such assumptions can be taken

c) If we are considering the clockwise direction to be positive then the rotation along the counter clockwise direction is also positive as no such assumptions can be taken

d) If we are considering the clockwise direction to be negative then the rotation along the counter clockwise direction is neither positive nor negative as we only pre assumed the clockwise direction

View Answer

Explanation: We can take such assumptions. We are free to do so. We just need to specify if clockwise is positive then the counter clockwise is to be negative. Also such an assumption are very useful in the 2D calculation of the moments caused by various forces on the body.

13. The doors are having hinges to support them. This hinge is too a type of bearing or is a Device which is using the effect like bearing to support. So, if you are opening the door, then the force you apply is greater if you open it from the part closer to the hinges.

a) True

b) False

View Answer

Explanation: As the moment is the product of the force and the perpendicular distance of the point of action and the axis, thus more the distance more will be the moment. And hence to overcome that you have to apply more energy. Thus the answer.

14. Which of the following is true for the bearing’s body?

a) Total moment of various forces acting on the body is the vector sum of all moments in 3D

b) Total moment of various forces acting on the body is the algebraic sum of all moments in 3D

c) Total moment of various forces acting on the body is always zero in any dimension

d) Total moment of various forces acting on the body is the vector sum of all moments which is perpendicular to each other forces whatever be the dimensions

View Answer

Explanation: When we consider about the dimensions we need to be careful. The moment is the vector quantity. Thus the value of the total moment caused by various forces acting on the body is the vector sum of all the vectors. Also, the moments are not perpendicular to each other unless it is specified.

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