# Engineering Mechanics Questions and Answers – Frictional Forces on Screws

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

1. In general cases the screws are used as __________
a) Fasteners
b) Main components
c) Simpler
d) Upstreamers

Explanation: The screws are generally used as the fasteners. The main thing about the screws is that the friction helps the holding of the structures. Also, screws help make the structure join fast and efficiently. Thus the name fasteners.

2. Which type of the screws are used in the machines?

Explanation: The square threaded screws are used in the machines. As the screws are generally used as the fasteners. The main thing about the screws is that the friction helps the holding of the structures. Also, screws help make the structure join fast and efficiently.

3. Why are square threaded screws are used in the machines?
a) Large forces act along the axis of the screws
b) Small forces act along the axis of the screws
c) Large forces act perpendicular the axis of the screws
d) Small forces act perpendicular the axis of the screws

Explanation: The square threaded screws are used in the machines. As these screws are generally used as the fasteners. The main thing about these screws is that the friction helps the holding of the structures. Also, screws help make the structure join fast and efficiently. And in these screws forces act along the axis of screws.

4. The angle of the threading in the screw is determined by which of the following trigonometric function?
a) Tangent Inverse
b) Sine
c) Cosine
d) Secant

Explanation: The angle of the threading in the screw is determined by inverse tangent trigonometric function. This is the generalized form of the function which is being used so as to get the value of the angle. In wedges, the same function is used so as to find the angle of a wedge.

5. In the determination of the angle of the screw, the ratio kept in the inverse tangent function is the ratio of ________
a) Vertical and Horizontal distance of the screw
b) Horizontal and Vertical distance of the screw
c) Vertical and Linear distance of the screw
d) Linear and Horizontal distance of the screw

Explanation: The angle of the threading in the screw is determined by inverse tangent trigonometric function. This is the generalised form of the function which is being used so as to get the value of the angle. In wedges, the same function is used so as to find the angle of a wedge. And in both, the case the ratio is vertical is to horizontal.

6. The horizontal distance used in the inverse trigonometry function is called as _____________
c) Major
d) Cut-off

Explanation: The angle of the threading in the screw is determined by inverse tangent trigonometric function. This is the generalized form of the function which is being used so as to get the value of the angle. In wedges, the same function is used so as to find the angle of a wedge. And thus the horizontal distance is called as lead.

7. In screws there is an application of two and three force members. The basic difference between the two and the three force members used 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

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.

8. Determine the moment of the force along point P (There is screw present at P, about which the rotation is there).

a) 110Nm
b) 112.5Nm
c) 60Nm
d) 0Nm

Explanation: As we know that the moment is the cross product of the distance and the force we will try to apply the same here. We see that the perpendicular distance is 1.5 (3cos60). Thus we get the distance. And hence multiply it with the force, 75×1.5. Because the force component perpendicular to the distance needs to be taken.

9. When we apply the equilibrium equations in the free body diagram of the screw, for two force members to be in equilibrium then _________
a) They both must not be collinear
b) They must be of different magnitude
c) They must be in the same direction
d) They must be in the opposite direction cancelling each other

Explanation: Simply, for the equilibrium the net force must be zero. That is the forces must be collinear if equilibrium is to be established. And they must be in the opposite directions. They also must be of the same magnitude, cancelling each other.

10. Which of the following statement for the three force system applied in the screws is true?
a) The moment need not to be seen for the equilibrium, they are always in equilibrium
b) The forces are not always in the equilibrium
c) The forces are always in equilibrium
d) The moments are always in equilibrium

Explanation: The forces in the three force system are not always in the equilibrium. The equilibrium is established when the forces cancel out each other. Also when the net moment is zero. Then only the equilibrium is established in the three force system.

11. Which of the following is correct for a screw being rotated?
a) The couple moment depends on the axis of rotation
b) The couple moment depends directly on the radius vector of forces
c) The couple moment depends only on the distance vector between the forces
d) The couple moment’s direction is given by the left hand rule

Explanation: The couple moment depends only on the distance vector between the forces. The radius vector of the forces are not making the couple depended over it. But the distance vector is driven by subtracting the radius vectors of the forces. This means that moment of the couple doesn’t directly depend on the radius vector of forces.

12. If the forces acting on the couple acting on the screw are in the same direction, that is they are not in the opposite direction as always they are, then?
a) The direction of the forces doesn’t determine the moment
b) The couple moment will be maximum
c) The couple is not possible
d) No change occurs

Explanation: The forces are always in the opposite direction for the couple moment. But if they don’t act like the same that is they change their directions and align themselves in the same direction then the couple is not possible.

13. For equilibrium, the net force acting on the screw is zero.
a) True
b) False

Explanation: The equilibrium is only attained if the net force on the body tends to be equal to zero. Thus the forces cancel out. If this happens there is no motion of the body along with any direction and hence the body is said to be in equilibrium. The body here is a rigid body.

14. In the screw collinear forces act, what is a collinear system of forces?
a) The force system having all the forces parallel to each other
b) The force system having all the forces perpendicular to each other
c) The force system having all the forces emerging from a single point
d) Forces cannot form a collinear system of forces, it is not possible

Explanation: The force system having all the forces emerging from a point is called the collinear system of force. This is a type of system of the force, which is easy in the simplification. This is because as the forces are the vector quantity, the vector math is applied and the simplification is done.

15. Determine the smallest force applied at R which creates the same moment about P as by 75N. (There is a presence of screw at P, about which the rotation is being there)

a) 37.5N
b) 112.5N
c) 60N
d) 0N

Explanation: As we know that the moment is the cross product of the distance and the force we will try to apply the same here. We see that the perpendicular distance is 3m. Thus we get the distance. And hence multiply it with the force, the moment = 112.5Nm. Because the force component perpendicular to the distance needs to be taken.

Sanfoundry Global Education & Learning Series – Engineering Mechanics.

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