# Engineering Mechanics Questions and Answers – Two and Three Force Members

This set of Engineering Mechanics Multiple Choice Questions & Answers (MCQs) focuses on “Two and Three Force Members”.

1. 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

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.

2. Determine the vertical components of the reaction on the beam at pin Q.

a) 4kN
b) 3kN
c) 2kN
d) 1kN

Explanation: The summation of the forces needs to be zero. So does the summation of the moments need to zero. But talking about the angles, they not needed to zero. But the forces which are acting at particular angles, must needed to be equal to zero. The basic need of the forces to make the body in equilibrium.

3. Which of the following is correct?
a) The two force members doesn’t apply the moments to the body
b) The three force members doesn’t apply the moments to the body
c) Only the two force members apply the moments to the body
d) Both the three and two force members apply the moments to the body

Explanation: The force members doesn’t define whether the moment will be applied or not. They are basically the forces only. Thus if there is a force applied on the body, there will be a moment produced by them. If not then probably the forces might be collinear.
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4. The three member forces are greatly influencing the moment than the two force members.
a) True
b) False

Explanation: The influence of the moment on the body is determined by the number of the forces acting on the body. It depend on the magnitude of the force. It also depends whether the forces are collinear or not. Thus the number of forces are not the only parameter for the determination of the moment.

5. The three member forces apply three different moments and the two members apply two different moments on the body.
a) True
b) False

Explanation: Never judge the application of the moment of the force applied on the body by the number of the forces being acted on the body. What is two of the forces becomes collinear and are having a zero distance from the axis of rotation. Thus the three and two force member apply moments according to the situation, whether the distance is zero or not.

6. For two force members to be in equilibrium when _____________
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 same magnitude, cancelling each other.

7. Determine the force in section RS.

a) 11.3N
b) 3kN
c) 2kN
d) 1kN

Explanation: The summation of the forces needs to be zero. So does the summation of the moments need to zero. But talking about the angles, they not needed to zero. But the forces which are acting at particular angles, must needed to be equal to zero. The basic need of the forces to make the body in equilibrium.

8. Moment equilibrium for the three force members will only be satisfied if_____________
a) Three forces are in different dimensions
b) The forces are in the same direction
c) The forces are concurrent
d) The forces are perpendicular

Explanation: The moment equilibrium for the three force members is satisfied only when the three forces are concurrent. That is the forces form a parallel system. That is the net force on the three axis turns out to be zero. This will only happen if the forces are in the same plane.

9. Which of the following statement for the three force system is true?
a) The moment need not 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 is 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.

10. Determine the horizontal components of the reaction on the beam at pin Q.

a) 8kN
b) 3kN
c) 2kN
d) 1kN

Explanation: None.

11. Determine the magnitude of the force F = 300j parallel to the direction of AB?

a) 155N
b) 257.1N
c) 200N
d) 175N

Explanation: Force component in the direction parallel to the AB is given by unit vector 0.286i + 0.857j + 0.429k. Now (300j).(0.286i + 0.857j + 0.429k) = 257.1N. Just try to resolve the force into it’s particular components.

12. All the forces need to be collinear in the three force system. Then only they will for the equilibrium state.
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

Explanation: The forces need to be collinear. If they are not so then the equilibrium is not possible. If they are parallel too, then it is assumed that they are meeting in the infinity. And hence the equilibrium is established between the forces. Thus the forces must be collinear.

13. Determine the vertical components of the reaction on the beam at pin Q.

a) 4kN
b) 3kN
c) 2kN
d) 1kN

Explanation: None.

14. The three force system can also be in the equilibrium if_________
a) All the forces are parallel to each other heading towards the same direction
b) The force components cancel each other
c) The forces are very small in magnitude
d) The forces are very huge in magnitude

Explanation: Even if the forces components cancels each other than the body is said to be in equilibrium. Also, it should satisfy whether the moments caused by the forces are equal to zero or not. This means if the moment caused and the net force is zero the body is in equilibrium.

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