# Engineering Mechanics Questions and Answers – Conditions for a Rigid-Body Equilibrium – 1

This set of Engineering Mechanics Multiple Choice Questions & Answers (MCQs) focuses on “Conditions for a Rigid-Body Equilibrium – 1”.

1. The main condition for the rigid body is that the distance between various particles of the body does change.
a) True
b) False

Explanation: The main condition for the rigid body is that the distance between various particles of the body does not change. If the distance does change the body is not to be called as rigid. Thus the fix distance of the particles is very much required for the equilibrium of the rigid body.

2. The shown here has a mass of 100kg. What is missing here in the diagram?

a) The weight of the body is not shown
b) The moment of the force is not shown
c) The body cant be held like this
d) The body diagonal is not shown

Explanation: None.

3. What does Newton’s third law states?
a) The rate of change of momentum is equal to the force applied
b) For every reaction, there is an opposite reaction
c) The body tends to be rotated if the force is applied tangentially
d) The body is rest until a force is applied

Explanation: The requirement of the third law is important in the equilibrium of the body. Especially the rigid bodies. The rigid body particles are in the equilibrium and are thus facing the forces and to be in the equilibrium they also react and apply the opposite force and thus the third law of Newton.

4. Determine the horizontal components of the reaction on the beam caused by the pin at P. The force 60N is multiplied by 10 and then is applied.

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a) 424N
b) 24N
c) 44N
d) 441N

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 be needed to be equal to zero. The basic need of the forces to make the body in equilibrium.

5. For equilibrium, the net force acting on the body 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.

6. For equilibrium, the net moment acting on the body by various forces is zero.
a) True
b) False

Explanation: The equilibrium is only attained if the net moment on the body tends to be equal to zero. Thus the moments caused by different 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.

7. Determine the vertical components of the reaction on the beam caused by the pin at Q. The force 60N is multiplied by 10 and then is applied.

a) 319N
b) 445N
c) 45N
d) 40N

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. The net moment of the body is zero that means the distance between the force and the rotational axis is zero.
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 net moment of the body is zero that doesn’t mean that the distance between the force and the rotational axis is zero. This means moments caused by different forces cancels 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.

9. Determine the horizontal components of the reaction on the beam caused by the roller at P.

a) 536N
b) 536cos30N
c) 536sin30N
d) 536tan30N

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 need to be equal to zero. The basic need of the forces to make the body in equilibrium.

10. The net force of the body is zero that means the force are not being applied to the body at all and hence the body is in equilibrium.
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 net force of the body is zero that doesn’t mean that the force are not being applied to the body at all and hence the body is in equilibrium. The equilibrium is only attained if the net force on the body tends to be equal to zero. Thus the forces cancels out. If this happens there is no motion of the body along any direction and hence the body is said to be in equilibrium.

11. Which of the following is correct?
a) The application of the conditions of the equilibrium of the body is valid only in the 2D
b) The application of the conditions of the equilibrium of the body is valid only in the 3D
c) The application of the conditions of the equilibrium of the body is valid only in the 1D
d) The application of the conditions of the equilibrium of the body is valid throughout

Explanation: The application of the conditions of the equilibrium of the body is valid throughout. This means that the conditions are irrespective of the dimensions. The conditions are the basic rules that define the equilibrium of the body and thus are applicable in any dimension of the real axis.

12. Determine the vertical components of the reaction on the beam caused by the roller at P.

a) 536N
b) 536cos30N
c) 536sin30N
d) 536tan30N

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 need to be equal to zero. The basic need of the forces to make the body in equilibrium.

13. For the conditions of the equilibrium of the body, i.e. the rigid body only the external forces defines the equilibrium. Because the internal forces cancels out so not to be considered.
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 application of the internal forces does affect the conditions of the equilibrium of the body. Not only the external but the internal forces that are developed by the sake of external forces does develop a tending effect on the equilibrium of the body. Thus the internal forces doesn’t cancels out.

14. Which of the following needs to zero for the perfect equilibrium?
a) ∑F=0, ∑M=0 and ∑θ = 0
b) ∑F=0, ∑M≠0 and ∑θ = 0
c) ∑F≠0, ∑M=0 and ∑θ = 0
d) ∑F=0, ∑M=0 and ∑θ≠0

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 need to be equal to zero. The basic need of the forces to make the body in equilibrium.

15. Determine the vertical components of the reaction on the beam caused by the pin at P. The force 60N is multiplied by 10 and then is applied.

a) 405N
b) 445N
c) 45N
d) 40N

Explanation: None.

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