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# MCQs on Method of Sections

We use the method of joints when the members on which the force to be found are few in number.

a) True

b) False

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Answer: a

Explanation: For few members we use method of joints to find the unknown force. It defines as if the whole truss is in equilibrium then all the joints which are connected to that truss is in equilibrium. This is known as method of joints. But when the system becomes complex, method of section comes into the picture.

The method of section cuts the whole structure of trusses into section and then uses the cut out portion for the calculations.

a) True

b) False

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Answer: a

Explanation: The method of section cuts the whole structure of trusses into section and then uses the cut out portion for the calculations. In which the net force equals zero equation is used. The net moment is made to be zero, etc. All these conditions of equilibrium is applied.

The method of joints helps us to find out the unknown force in the trusses joint. And the method of section helps us to make the calculation of the direction of the zero members.

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

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Answer: c

Explanation: Method of joints defines as if the whole truss is in equilibrium then all the joints which are connected to that truss is in equilibrium. While the method of section cuts the whole structure of trusses into section and then uses the cut out portion for the calculations of the unknown forces. Thus both the methods are used for the same purpose.

Method of section cuts the whole structure of trusses into a section and then uses the cut out portion for the calculations of the unknown forces. For this method, at most two forces must be collinear.

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

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Answer: c

Explanation: Method of section cuts the whole structure of trusses into a section and then uses the cut out portion for the calculations of the unknown forces. For this method, we don’t require two forces to be collinear. But if the forces are collinear than the task of determining the unknown forces is very easy.

The determination of the truss’s support reaction is done first and then the section is isolated for the method of the section.

a) The first step is right but the second one is wrong

b) The first step is wrong and the second one is wrong too

c) The first step is right and the second one is right too

d) The first step is wrong but the second one is right

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Answer: c

Explanation: The determination of the force of the unknown element is done by the method of the section. For this the section is isolated from the main structure and then the calculation is done after. But before that the determination of the support reaction needs to be done.

Why the determination of the support reaction needs to be done before isolating the section?

a) This reduces the calculation and also the labour

b) This makes the isolated section more complicated

c) This results in reduction on the formulas used

d) This procedure is not done at all, it of no need

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Answer: a

Explanation: The determination of the force of the unknown element is done by the method of section. For this the section is isolated from the main structure and then calculation is done after. But before that the determination of the support reaction needs to be done.

The free diagram of the section of the truss is made for the section having the least number of the forces. This is done as to make the calculations easy.

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

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Answer: d

Explanation: The part of the calculation is made easier if the flow diagram of that section is made which is having the least number of forces. Thus for the sake of the calculation this is done. Or one can say that for getting the unknown force we use this method.

We have three method to solve for the unknown force in the trusses. They are method of section, method of joints and rotational vector method.

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

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Answer: b

Explanation: The main methods for the solving for the unknown force on the truss are method of section and the method of joints. The other method is just given for the sake of confusion. This means that only two main methods are to applied for solving the unknown force on a truss.

The free body diagram of which part of the section of the truss is made to make use of the method of sections?

a) Joints

b) Truss

c) The whole structure

d) Any section can be used

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Answer: d

Explanation: The free body diagram of any part of the section of the truss is made to make use of the method of sections. Various equations of equilibrium are made to do the calculations. The net force acting on the vertical direction is made zero. Also, horizontal direction forces are made to be zero.

Determine the force in members UT.

a) 1980N

b) 800N

c) 2200N

d) 1100N

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Answer: b

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.

Determine the force in members UR.

a) 1980N

b) 800N

c) 2200N

d) 1100N

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Answer: a

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.

Determine the force in members QR.

a) 1980N

b) 800N

c) 2200N

d) 1100N

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Answer: c

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.

The system of the collinear and the parallel force are simplified as:

a) The simplified collinear force system gives us a net force and the parallel force system gives us a simplified force, and then we add it vectorially

b) Such simplification is not possible

c) The simplification is usually done by not considering the directions of the both

d) The simplification is done by considering the rotations only

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Answer: a

Explanation: The simplification is easy. The simplified force system gives us a net force and the parallel force system gives us a simplified force, and then we add it vectorially. Thus the vector addition at the last can be easily done and thus both can be simplified.