1. A couple consists of two forces that are:
A.
Equal and opposite, acting along the same line
B.
Equal and opposite, acting along parallel lines
C.
Unequal and parallel, acting in the same direction
D.
Perpendicular and unequal, acting at one point
Correct Answer:
Equal and opposite, acting along parallel lines
Explanation:
A couple is formed by two equal, opposite, and parallel forces whose lines of action are separated by a distance.
2. The moment of a couple is calculated using which expression?
A.
Force divided by arm length
B.
Force multiplied by arm length
C.
Force added to arm length
D.
Arm length divided by force
Correct Answer:
Force multiplied by arm length
Explanation:
The moment of a couple is equal to the product of either force and the perpendicular distance between their lines of action: M = Fd.
3. Two equal and opposite forces of 5 N form a couple with an arm of 0.4 m. What is the moment of the couple?
A.
1 N m
B.
2 N m
C.
5.4 N m
D.
12.5 N m
Correct Answer:
2 N m
Explanation:
The moment is M = Fd = 5 × 0.4 = 2 N m.
4. The net force of a pure couple is:
A.
Zero
B.
Equal to one of the forces
C.
Twice either force
D.
Always equal to the arm length
Correct Answer:
Zero
Explanation:
The two forces in a couple are equal and opposite, so their vector sum is zero.
5. The perpendicular distance between the lines of action of the two forces in a couple is called the:
A.
Radius of gyration
B.
Couple arm
C.
Displacement vector
D.
Lever velocity
Correct Answer:
Couple arm
Explanation:
The couple arm is the perpendicular distance between the lines of action of the equal and opposite forces.
6. A couple produces which effect on a rigid body when its net force is zero?
A.
Pure rotation
B.
Pure translation
C.
No effect at all
D.
Uniform expansion only
Correct Answer:
Pure rotation
Explanation:
Since the net force of a couple is zero but its moment is nonzero, it produces rotational motion without translation.
7. If the force in a couple is doubled while the couple arm remains unchanged, the moment of the couple becomes:
A.
Half
B.
Unchanged
C.
Double
D.
Four times
Correct Answer:
Double
Explanation:
Because M = Fd, doubling the force doubles the moment when the arm remains constant.
8. If the couple arm is doubled while the forces remain unchanged, the moment of the couple becomes:
A.
Half
B.
Unchanged
C.
Double
D.
Four times
Correct Answer:
Double
Explanation:
The moment of a couple is directly proportional to its arm, so doubling the arm doubles the moment.
9. The SI unit of the moment of a couple is:
A.
Newton
B.
Newton per metre
C.
Newton metre
D.
Kilogram per metre
Correct Answer:
Newton metre
Explanation:
Moment of a couple equals force multiplied by distance, so its SI unit is newton metre (N m).
10. The moment of a couple is independent of the:
A.
Magnitude of either force
B.
Distance between the force lines
C.
Point about which the moment is calculated
D.
Direction of rotation produced
Correct Answer:
Point about which the moment is calculated
Explanation:
For a couple, the net force is zero, so its moment has the same value about any point.
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