Moments, Couples, and Parallel Forces – Engineering Mechanics MCQs
Q1. Forces which act on the same plane are called
A) Coplanar forces
B) Non-coplanar forces
C) Concurrent forces
D) Collinear forces
Answer: A) Coplanar forces
Explanation: Coplanar forces lie in a single plane.
Q2. Forces which do not act in the same plane are called
A) Coplanar forces
B) Non-coplanar forces
C) Concurrent forces
D) Parallel forces
Answer: B) Non-coplanar forces
Explanation: Non-coplanar forces act in different planes.
Q3. When all forces pass through a single point, they are called
A) Parallel forces
B) Concurrent forces
C) Non-concurrent forces
D) Coplanar forces
Answer: B) Concurrent forces
Explanation: Concurrent forces meet at one common point.
Q4. Forces that do not pass through a common point are called
A) Concurrent
B) Non-concurrent
C) Collinear
D) Equal forces
Answer: B) Non-concurrent
Explanation: Non-concurrent forces have lines of action that do not meet.
Q5. Two or more forces whose lines of action are parallel are called
A) Parallel forces
B) Concurrent forces
C) Non-coplanar forces
D) Equal forces
Answer: A) Parallel forces
Explanation: In parallel forces, all forces are parallel to each other.
Q6. Coplanar concurrent forces act
A) In one plane and meet at a point
B) In different planes
C) In one plane but do not meet
D) At right angles
Answer: A) In one plane and meet at a point
Explanation: Coplanar concurrent = same plane and same point.
Q7. Coplanar non-concurrent forces act
A) In one plane and meet at a point
B) In one plane but do not meet at a point
C) In different planes
D) At right angles
Answer: B) In one plane but do not meet at a point
Explanation: Non-concurrent = no common point of intersection.
Q8. Non-coplanar concurrent forces act
A) In one plane and meet at a point
B) In different planes but meet at one point
C) In one plane and parallel
D) In different planes and do not meet
Answer: B) In different planes but meet at one point
Explanation: They intersect at a point but are not in same plane.
Q9. Non-coplanar non-concurrent forces act
A) In one plane and meet at a point
B) In one plane but do not meet
C) In different planes and do not meet
D) In different planes and meet at a point
Answer: C) In different planes and do not meet
Explanation: Neither in one plane nor intersecting.
Q10. The resultant of concurrent forces passes through
A) The center of gravity
B) The common point of concurrency
C) The midpoint of the forces
D) The centroid of the system
Answer: B) The common point of concurrency
Explanation: Resultant of concurrent forces always acts through same point.
Q11. The best example of concurrent forces is
A) Weight, normal reaction, tension at a hanging body
B) Pressure on a wall
C) Two parallel loads on a beam
D) Moment of a couple
Answer: A) Weight, normal reaction, tension at a hanging body
Explanation: All meet at one common point.
Q12. The forces acting on the supports of a simply supported beam are
A) Concurrent
B) Parallel and non-concurrent
C) Coplanar concurrent
D) Collinear
Answer: B) Parallel and non-concurrent
Explanation: Reactions act vertically, parallel, and do not meet.
Q13. Coplanar parallel forces produce
A) Resultant only
B) Only moment
C) Both resultant and moment
D) Zero resultant
Answer: C) Both resultant and moment
Explanation: Parallel forces cause translation and rotation.
Q14. The weight of an object and the normal reaction on it are
A) Concurrent
B) Parallel and opposite
C) Coplanar concurrent
D) Perpendicular concurrent
Answer: B) Parallel and opposite
Explanation: They act along same line but in opposite directions.
Q15. The forces acting on the threads of a hanging lamp are
A) Concurrent
B) Non-concurrent
C) Parallel
D) Coplanar non-concurrent
Answer: A) Concurrent
Explanation: All tensions and weight meet at one point.
Q16. When three forces keep a body in equilibrium, they must be
A) Non-coplanar
B) Coplanar and concurrent
C) Coplanar and parallel
D) Non-concurrent
Answer: B) Coplanar and concurrent
Explanation: For equilibrium, three forces must meet at a point and lie in same plane.
Q17. Forces in a truss joint are
A) Non-concurrent
B) Coplanar and concurrent
C) Parallel
D) Non-coplanar
Answer: B) Coplanar and concurrent
Explanation: All forces at a truss joint meet at one point.
Q18. If several concurrent forces are in equilibrium, their vector sum is
A) One
B) Infinite
C) Zero
D) Equal to resultant
Answer: C) Zero
Explanation: For equilibrium, ΣF = 0.
Q19. The resultant of two concurrent forces depends on
A) Their magnitude only
B) Their direction only
C) Both magnitude and angle between them
D) None
Answer: C) Both magnitude and angle between them
Explanation: Resultant R = √(P² + Q² + 2PQcosθ).
Q20. For coplanar concurrent forces, the conditions of equilibrium are
A) ΣFx = 0, ΣFy = 0
B) ΣM = 0 only
C) ΣF = 0 only
D) ΣFx = ΣFy = ΣM = 0
Answer: A) ΣFx = 0, ΣFy = 0
Explanation: No moment condition since all pass through one point.
Q21. The lines of action of three concurrent forces intersect at
A) Different points
B) Same point
C) Parallel lines
D) None
Answer: B) Same point
Explanation: Concurrent means intersecting at one common point.
Q22. The coplanar forces which do not intersect but their lines of action are parallel are called
A) Collinear forces
B) Non-concurrent parallel forces
C) Non-coplanar forces
D) Concurrent forces
Answer: B) Non-concurrent parallel forces
Explanation: They are parallel but not meeting at a single point.
Q23. The reaction of a smooth wall is always
A) Tangential
B) Perpendicular to wall
C) Inclined at 45°
D) Along wall surface
Answer: B) Perpendicular to wall
Explanation: Smooth surface gives normal reaction only.
Q24. The tension in two strings supporting a load at a point represent
A) Non-concurrent forces
B) Concurrent forces
C) Parallel forces
D) Collinear forces
Answer: B) Concurrent forces
Explanation: All meet at the point of suspension.
Q25. Non-coplanar forces have
A) Single plane of action
B) Multiple planes of action
C) No resultant
D) Same line of action
Answer: B) Multiple planes of action
Explanation: They lie in different planes.
Q26. In a three-dimensional structure, forces acting along different planes are called
A) Coplanar
B) Non-coplanar
C) Concurrent
D) Collinear
Answer: B) Non-coplanar
Explanation: Not restricted to one plane.
Q27. The resultant of two non-concurrent forces can be found by
A) Parallelogram law
B) Triangle law
C) Polygon law
D) Both A and B
Answer: D) Both A and B
Explanation: Both are vector methods to find resultant.
Q28. The line of action of the resultant in non-concurrent forces does not pass through
A) The same point as all forces
B) The centroid
C) The line of each force
D) The axis of symmetry
Answer: A) The same point as all forces
Explanation: Non-concurrent means resultant line is different.
Q29. The moment of a concurrent force about its point of concurrency is
A) Zero
B) Infinite
C) Maximum
D) None
Answer: A) Zero
Explanation: Since its line passes through that point.
Q30. Coplanar concurrent force system exists in
A) Beams
B) Frames
C) Joints of trusses
D) Shafts
Answer: C) Joints of trusses
Explanation: All forces meet at a joint and lie in one plane.
Q31. A body is said to be in equilibrium when
A) It moves at constant speed
B) The resultant force is zero
C) It is rotating uniformly
D) It is stationary only
Answer: B) The resultant force is zero
Explanation: For equilibrium, net force acting on the body must be zero.
Q32. If a body is in equilibrium under the action of three forces, these forces must be
A) Parallel
B) Concurrent and coplanar
C) Non-concurrent
D) Equal in magnitude
Answer: B) Concurrent and coplanar
Explanation: Three forces equilibrium condition requires them to be concurrent and coplanar.
Q33. The law of parallelogram of forces is applicable only when forces are
A) Non-coplanar
B) Coplanar and concurrent
C) Parallel
D) Unequal
Answer: B) Coplanar and concurrent
Explanation: It applies when forces act at a point in one plane.
Q34. According to Lami’s theorem, if three forces keep a body in equilibrium, then
A) F1/sinA = F2/sinB = F3/sinC
B) F1/F2 = F2/F3 = F3/F1
C) F1 × F2 × F3 = 0
D) None of these
Answer: A) F1/sinA = F2/sinB = F3/sinC
Explanation: Lami’s theorem gives relation among three concurrent forces in equilibrium.
Q35. The polygon law of forces is used when
A) Two forces act
B) Three forces act
C) More than two forces act
D) Only one force acts
Answer: C) More than two forces act
Explanation: Polygon law extends the triangle law to any number of forces.
Q36. For equilibrium of concurrent coplanar forces, the conditions are
A) ΣFx = 0 and ΣFy = 0
B) ΣFx = 0 only
C) ΣM = 0 only
D) ΣFy = 0 only
Answer: A) ΣFx = 0 and ΣFy = 0
Explanation: The sum of horizontal and vertical components must be zero.
Q37. The body under three forces in equilibrium forms
A) A parallelogram
B) A triangle
C) A square
D) A rectangle
Answer: B) A triangle
Explanation: The three forces can be represented by the sides of a triangle.
Q38. In Lami’s theorem, the angle opposite to each force is
A) The included angle between other two forces
B) 90°
C) 45°
D) None
Answer: A) The included angle between other two forces
Explanation: Each force is opposite to the angle between the other two.
Q39. A beam resting on two supports with a central load has
A) Non-concurrent parallel forces
B) Concurrent coplanar forces
C) Non-coplanar forces
D) Concurrent non-coplanar forces
Answer: A) Non-concurrent parallel forces
Explanation: Reactions are parallel and don’t meet.
Q40. The equilibrium of a particle is classified as
A) Static and dynamic
B) Coplanar and non-coplanar
C) Linear and rotational
D) Translational and rotational
Answer: A) Static and dynamic
Explanation: Static when at rest, dynamic when moving with constant velocity.
Q41. The algebraic sum of the moments of all forces about any point in equilibrium is
A) Zero
B) One
C) Constant
D) Infinite
Answer: A) Zero
Explanation: ΣM = 0 is the rotational equilibrium condition.
Q42. For a system of coplanar non-concurrent forces to be in equilibrium
A) ΣFx = ΣFy = ΣM = 0
B) ΣFx = 0 only
C) ΣFy = 0 only
D) ΣM = 0 only
Answer: A) ΣFx = ΣFy = ΣM = 0
Explanation: Translational and rotational equilibrium both required.
Q43. The triangle law of forces is used for
A) Two concurrent forces
B) Three concurrent forces
C) Non-concurrent forces
D) Parallel forces
Answer: B) Three concurrent forces
Explanation: The three forces can form a triangle in equilibrium.
Q44. The principle of transmissibility of forces states that
A) Force can act anywhere on body
B) Line of action can be shifted without changing effect
C) Force changes its direction when transmitted
D) None
Answer: B) Line of action can be shifted without changing effect
Explanation: As long as line of action remains same, effect is unchanged.
Q45. For a system in equilibrium, resultant of all forces and moments is
A) Equal to zero
B) Equal to weight
C) Equal to tension
D) Equal to mass
Answer: A) Equal to zero
Explanation: Both resultant force and resultant moment must be zero.
Q46. The number of equilibrium equations in 2D force system is
A) 1
B) 2
C) 3
D) 4
Answer: C) 3
Explanation: ΣFx = 0, ΣFy = 0, ΣM = 0.
Q47. When a body is in static equilibrium,
A) It is at rest
B) It moves at constant speed
C) It accelerates uniformly
D) None
Answer: A) It is at rest
Explanation: Static equilibrium means zero velocity.
Q48. Dynamic equilibrium means
A) Constant acceleration
B) Constant velocity
C) Body at rest
D) Body under unbalanced forces
Answer: B) Constant velocity
Explanation: Forces balance out though body is in motion.
Q49. A ladder resting against a smooth wall is an example of
A) Equilibrium of concurrent forces
B) Equilibrium of non-concurrent forces
C) Non-coplanar forces
D) Coplanar concurrent forces
Answer: B) Equilibrium of non-concurrent forces
Explanation: Forces act in one plane but don’t meet at one point.
Q50. When a body is acted upon by two equal and opposite forces, the body
A) Moves
B) Rotates
C) Remains in equilibrium
D) Deforms
Answer: C) Remains in equilibrium
Explanation: Equal and opposite forces cancel each other.
Q51. The line of action of the resultant passes through
A) The point of concurrency
B) Centroid of the system
C) Any arbitrary point
D) None
Answer: A) The point of concurrency
Explanation: For concurrent forces, resultant passes through same point.
Q52. The moment of a force about any point is
A) Product of force and perpendicular distance
B) Sum of all forces
C) Equal to zero always
D) None
Answer: A) Product of force and perpendicular distance
Explanation: M = F × d.
Q53. The principle of moments is also known as
A) Lami’s theorem
B) Varignon’s theorem
C) Triangle law
D) Polygon law
Answer: B) Varignon’s theorem
Explanation: It relates the moment of a resultant to the sum of moments of components.
Q54. Varignon’s theorem is used for
A) Finding resultant
B) Finding moments
C) Finding friction
D) Finding torque
Answer: B) Finding moments
Explanation: It helps determine moment of a resultant force.
Q55. The resultant of two equal forces inclined at 120° is
A) Equal to one of the forces
B) Zero
C) Twice the force
D) Half the force
Answer: A) Equal to one of the forces
Explanation: R = √(F² + F² + 2F²cos120) = F.
Q56. If two equal forces are acting opposite to each other, the resultant is
A) Sum of both
B) Zero
C) Difference of both
D) Twice one
Answer: B) Zero
Explanation: Equal and opposite forces cancel each other.
Q57. The graphical representation of forces is done using
A) Force polygon
B) Moment diagram
C) Pressure diagram
D) Force table
Answer: A) Force polygon
Explanation: Force polygon shows equilibrium or resultant of several forces.
Q58. The polygon law of forces states that if several forces acting on a body can be represented in magnitude and direction by the sides of a polygon taken in order, then
A) They are in equilibrium
B) They are concurrent
C) They are equal
D) They are parallel
Answer: A) They are in equilibrium
Explanation: Closed polygon indicates no resultant.
Q59. In equilibrium, the closing side of the force polygon is
A) Zero
B) The resultant
C) Equal to any one side
D) None
Answer: A) Zero
Explanation: Closed polygon means resultant is zero.
Q60. The condition ΣM = 0 ensures
A) Rotational equilibrium
B) Translational equilibrium
C) Dynamic equilibrium
D) Linear equilibrium
Answer: A) Rotational equilibrium
Explanation: No net moment → no rotation.
Q61. When all forces acting on a body are balanced, the resultant is
A) Positive
B) Zero
C) Infinite
D) Equal to weight
Answer: B) Zero
Explanation: Balanced forces give zero resultant.
Q62. If two concurrent forces act at right angles, resultant is
A) P + Q
B) √(P² + Q²)
C) P – Q
D) 2PQ
Answer: B) √(P² + Q²)
Explanation: From parallelogram law.
Q63. For three coplanar concurrent forces in equilibrium, their vector sum is
A) Zero
B) Constant
C) Maximum
D) Equal to resultant
Answer: A) Zero
Explanation: ΣF = 0 condition of equilibrium.
Q64. The equilibrium of non-concurrent forces requires
A) ΣFx = ΣFy = ΣM = 0
B) ΣF = 0 only
C) ΣM = 0 only
D) ΣFx = 0 only
Answer: A) ΣFx = ΣFy = ΣM = 0
Explanation: Translation and rotation both must be balanced.
Q65. For a body under coplanar forces, the line of action of resultant can be found by
A) Taking moments about a point
B) Taking forces directly
C) Taking angle between forces
D) None
Answer: A) Taking moments about a point
Explanation: Moment helps locate the resultant position.
Q66. A closed force polygon represents
A) A body in equilibrium
B) A rotating body
C) A moving body
D) A non-equilibrium condition
Answer: A) A body in equilibrium
Explanation: Closed polygon → no resultant.
Q67. If a number of coplanar forces act on a rigid body, the body will be in equilibrium if
A) The algebraic sum of forces and moments are zero
B) The sum of forces is constant
C) The moments are maximum
D) None
Answer: A) The algebraic sum of forces and moments are zero
Explanation: Both translational and rotational balance are necessary.
Q68. The term “moment” means
A) Turning effect of force
B) Time duration of force
C) Linear motion
D) Angular velocity
Answer: A) Turning effect of force
Explanation: Moment causes rotation.
Q69. The resultant of two equal opposite parallel forces is
A) Zero
B) Couple
C) Same as one force
D) Sum of both
Answer: B) Couple
Explanation: Equal opposite parallel forces form a couple.
Q70. If the line of action of the resultant passes through the centroid of the force system, the system is said to be
A) Balanced
B) Unstable
C) Moment free
D) Central
Answer: D) Central
Explanation: Resultant passes through geometric center — called central force system.
Q71. The moment of a force about a point is the product of
A) Force and distance along the line of action
B) Force and perpendicular distance from the point
C) Force and radius
D) Force and time
Answer: B) Force and perpendicular distance from the point
Explanation: Moment = Force × perpendicular distance.
Q72. The SI unit of moment is
A) Newton
B) Newton-metre
C) Joule
D) Pascal
Answer: B) Newton-metre
Explanation: Moment is measured in N·m.
Q73. The moment of a force tends to
A) Translate the body
B) Rotate the body
C) Stop the body
D) Balance the body
Answer: B) Rotate the body
Explanation: Moment produces rotational effect about a point.
Q74. The perpendicular distance from the point to the line of action of a force is called
A) Moment arm
B) Torque
C) Resultant
D) Axis of rotation
Answer: A) Moment arm
Explanation: It is the lever arm or shortest distance.
Q75. The algebraic sum of moments about a point is zero for
A) Rotating body
B) Body in equilibrium
C) Moving body
D) Deforming body
Answer: B) Body in equilibrium
Explanation: ΣM = 0 is the condition for rotational equilibrium.
Q76. When two equal and opposite forces act on a body but not along the same line, they form a
A) Resultant force
B) Couple
C) Parallel system
D) Concurrent system
Answer: B) Couple
Explanation: Equal and opposite forces with parallel lines form a couple.
Q77. The moment of a couple is equal to
A) Product of one force and distance between forces
B) Sum of both forces
C) Product of resultant and radius
D) Zero
Answer: A) Product of one force and distance between forces
Explanation: Moment of couple = F × distance.
Q78. The resultant of a couple is
A) Equal to one of the forces
B) Zero
C) Double of one force
D) Sum of both forces
Answer: B) Zero
Explanation: Forces cancel translational effect but produce rotation.
Q79. A couple produces
A) Translational motion
B) Rotational motion only
C) Both rotation and translation
D) No effect
Answer: B) Rotational motion only
Explanation: A couple causes pure rotation.
Q80. The SI unit of moment of couple is
A) Joule
B) Newton-metre
C) Dyne-cm
D) kgf-m
Answer: B) Newton-metre
Explanation: Same as moment, N·m.
Q81. The direction of the moment of a couple is given by
A) Right-hand rule
B) Left-hand rule
C) Fleming’s rule
D) Both hands
Answer: A) Right-hand rule
Explanation: Curl fingers in direction of rotation; thumb shows moment direction.
Q82. A couple is a system of forces whose resultant is
A) One force
B) A single torque
C) Zero
D) None
Answer: C) Zero
Explanation: Translational effect is zero; only torque remains.
Q83. The total moment of several coplanar couples is equal to
A) The algebraic sum of their moments
B) The vector sum of forces
C) The resultant couple
D) None
Answer: A) The algebraic sum of their moments
Explanation: Moments can be added algebraically for coplanar couples.
Q84. When the resultant of two equal opposite parallel forces is zero but moment exists, it is called
A) Rotational system
B) Couple
C) Parallel system
D) Coplanar forces
Answer: B) Couple
Explanation: Equal and opposite parallel forces form a couple.
Q85. The point about which the moment is taken is called
A) Axis
B) Arm
C) Reference point or moment center
D) Center of mass
Answer: C) Reference point or moment center
Explanation: The point about which turning effect is calculated.
Q86. The unit of moment in CGS system is
A) Dyne-cm
B) Newton-metre
C) Joule
D) kgf-m
Answer: A) Dyne-cm
Explanation: In CGS, 1 dyne × 1 cm = 1 dyne-cm.
Q87. Two equal forces acting in opposite directions but not in same line constitute
A) Concurrent forces
B) Couple
C) Non-concurrent forces
D) Collinear forces
Answer: B) Couple
Explanation: Parallel but opposite forces separated by distance form a couple.
Q88. The effect of a couple on a rigid body is
A) Translational
B) Rotational
C) Both translational and rotational
D) None
Answer: B) Rotational
Explanation: Couples produce only rotation.
Q89. The net moment of a couple system acting on a rigid body is independent of
A) Magnitude of forces
B) Distance between forces
C) Position of couple
D) Direction of forces
Answer: C) Position of couple
Explanation: Moment of a couple is same about any point.
Q90. The algebraic sum of moments of a couple taken about any point is
A) Zero
B) Equal to the moment of couple
C) Depends on reference
D) Half the moment
Answer: B) Equal to the moment of couple
Explanation: Moment of couple is same about any point.
Q91. The sense or direction of a couple is determined by
A) Direction of one of its forces
B) Right-hand screw rule
C) Angle between forces
D) Line of action
Answer: B) Right-hand screw rule
Explanation: Curling fingers show rotation; thumb indicates couple direction.
Q92. Parallel forces acting in the same direction are known as
A) Like parallel forces
B) Unlike parallel forces
C) Concurrent forces
D) Coplanar forces
Answer: A) Like parallel forces
Explanation: All parallel and act in same direction.
Q93. Parallel forces acting in opposite directions are called
A) Like parallel forces
B) Unlike parallel forces
C) Coplanar forces
D) Collinear forces
Answer: B) Unlike parallel forces
Explanation: Opposite parallel forces are unlike parallel forces.
Q94. The perpendicular distance between two like parallel forces is known as
A) Arm of couple
B) Lever arm
C) Moment arm
D) None
Answer: C) Moment arm
Explanation: Distance between lines of action used to find moment.
Q95. When two like parallel forces act, the resultant lies
A) Between the two forces
B) Outside the forces
C) At midpoint always
D) None
Answer: A) Between the two forces
Explanation: Resultant lies closer to larger force.
Q96. When two unlike parallel forces act, the resultant lies
A) Between the two forces
B) Outside the two forces
C) At midpoint
D) None
Answer: B) Outside the two forces
Explanation: For opposite direction, resultant is external.
Q97. The magnitude of resultant of two parallel forces is
A) Sum of forces
B) Difference of forces
C) Depends on direction
D) Both A and B depending on direction
Answer: D) Both A and B depending on direction
Explanation: Like → sum, Unlike → difference.
Q98. A system of two equal opposite parallel forces separated by distance ‘d’ produces
A) Moment = F × d
B) Resultant = 0, Moment = F × d
C) Resultant = F, Moment = 0
D) Resultant = 2F, Moment = 2Fd
Answer: B) Resultant = 0, Moment = F × d
Explanation: Couple has zero resultant and finite moment.
Q99. In a parallel force system, if the resultant passes through the centroid of two forces, both forces must be
A) Equal and unlike
B) Equal and like
C) Unequal
D) Perpendicular
Answer: B) Equal and like
Explanation: Equal like forces act symmetrically.
Q100. The condition for equilibrium of parallel forces is
A) Sum of upward forces = sum of downward forces
B) ΣM = 0
C) Both A and B
D) None
Answer: C) Both A and B
Explanation: Translational and rotational equilibrium both required.
