# Engineering Mechanics Questions and Answers – Work – 2

This set of Engineering Mechanics Assessment Questions and Answers focuses on “Work – 2”.

1. Work done is best given by___________
a) dU = Fdrcosθ
b) dU = Fdrsinθ
c) dU = Fdrcotθ
d) dU = Fdrdθ

Explanation: The work is defined as the dot product of the force and the distance. This means that the work done does depends upon the angle of the force. That is the angle which is being made by the force vector to the surface of action of the force.

2. Calculate the Normal force developed between the body and the surface due to the work done by the force.

a) 611N
b) 116N
c) 100N
d) 180N

Explanation: The net forces acting on the body is shown with the help of the resultant forces. There are two types, first the frictional and the second is normal. This is because the resultant forces have the sum of all the forces which are acting in the direction which is same.

3. The supports in the 3D are having more than three reaction forces. Because they are having three axis on which the components of the work needs to be 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: As 3D is defined as the three axis system, we have to consider the equilibrium in all the three axis. This will make the equilibrium go on all the axis of the 3D space. And hence will cancel all the forces.

4. ∑Fx=0, ∑Fy=0 and ∑Fz=0 are vector equations for the three dimensions. They are satisfied when the body is achieved it state of equilibrium and the network done is zero.
a) True
b) False

Explanation: The answer is false as the equations asked are scalars. As we make the net sum of the forces along the axis equal to zero. Of course this equation comes from the solving the vector forms, but still the result is a scalar, hence the equations are scalar.

5. Calculate the frictional force developed between the body and the surface due to the work done by the force.

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a) 160N
b) 16N
c) 10N
d) 180N

Explanation: The net forces acting on the body is shown with the help of the resultant forces. There are two types, first the frictional and the second is normal. This is because the resultant forces have the sum of all the forces which are acting in the direction which is same.

6. Work done is best given by _____________
a) dU = F.dr
b) dU = Fdrsinθ
c) dU = F.drcotθ
d) dU = Fxdrdθ

Explanation: The work is defined as the dot product of the force and the distance. This means that the work done does depends upon the angle of the force. That is the angle which is being made by the force vector to the surface of action of the force.

7. We often determine the work done by the couples. A couple moment is developed when _______ of the attached member is prevented.
a) Translation
b) Rotation
d) Subtraction

Explanation: The development of the couple moment is when there is prevention of the rotation of the attached member. This is the basic condition for the equilibrium of the couple moments in any dimension. This rule is applied when the couple moments are taken into the account for the equilibrium of the body.

8. Work done by the couple is best given by___________
a) dU = Mdθ
b) dU = M.dθ
c) dU = Mxdθ
d) dU = Mθ

Explanation: The work done by the couple is defined as the product of the moment and the del angle. This means that the work done does depends upon the angle of the moment. That is the angle which is being made by the moment vector to the surface of action of the moment.

9. What is not the condition for the equilibrium in three dimensional system of axis so as to calculate the unknown forces acting on the body?
a) ∑Fx=0
b) ∑Fy=0
c) ∑Fz=0
d) ∑F≠0

Explanation: For the equilibrium in the three dimensional system of axis we have all the conditions true as, ∑Fx=0, ∑Fy=0 and ∑Fz=0. Also, we have the summation of the forces equal to zero. Which is not a non-zero value.

10. Virtual Work done is best given by_______________
a) δU = Fδrcosθ
b) δU = Fδrsinθ
c) δU = Fδrcotθ
d) δU = Fδrδθ

Explanation: The work is defined as the dot product of the δ force and the δ distance. This means that the work done does depends upon the angle of the force. That is the angle which is being made by the force vector to the surface of action of the force.

11. Virtual work done by the couple is best given by_____________
a) δU = Mδθ
b) δU = M.δθ
c) δU = Mxδθ
d) δU = Mθ

Explanation: The work done by the couple is defined as the product of the δ moment and the δ angle. This means that the work done does depends upon the angle of the moment. That is the angle which is being made by the moment vector to the surface of action of the moment.

12. Principle of virtual work done is having condition___________
a) δU = 0
b) δU = δF
c) δU = δM
d) δU = δD

Explanation: The virtual work done is working on the equation: δU = 0. This means that the body must be in the equilibrium and the network done must be zero. Thus the unknown forces are being determined by the same technique.

13. If solving the question in 3D calculations is difficult, then use the 2D system and then equate the total work done to zero.
a) True
b) False

Explanation: The answer is obviously yes. If we are having any difficulty in making the vector components, then we can go to 2D. As if the particle is in equilibrium, the net force will be zero. No matter where you see first. Network done is zero.

14. If the resolved force or the force which you get as the answer after solving the question is negative, then what does this implies?
a) The work done is in the reverse direction w.r.t the direction set in the free body diagram
b) The force is not in the reverse direction w.r.t the direction set in the free body diagram
c) The force component is not possible
d) The force is possible, but in the direction perpendicular to the resultant force

Explanation: The negative sign implies things are in the opposite manner. If the force is coming negative this doesn’t mean that it is impossible. But it means that the force is in the opposite direction w.r.t the direction set by you in the free body diagram.

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