1. The moment of a force is calculated about a specified point called the:
A.
Reference point
B.
Centre of mass
C.
Point of equilibrium
D.
Geometrical centre
Correct Answer:
Reference point
Explanation:
The moment of a force is always measured with respect to a chosen point, known as the reference point or origin.
2. If the reference point for calculating the moment of a force is changed, the moment may:
A.
Remain exactly the same in every case
B.
Change in magnitude
C.
Become equal to the force
D.
Always become zero
Correct Answer:
Change in magnitude
Explanation:
The moment arm depends on the reference point, so changing the reference point can change the moment of the force.
3. The moment of a force about a reference point is zero when the:
A.
Force is very large
B.
Reference point is far from the object
C.
Line of action of the force passes through the reference point
D.
Force acts horizontally
Correct Answer:
Line of action of the force passes through the reference point
Explanation:
When the line of action passes through the reference point, the perpendicular distance is zero, so the moment is zero.
4. A force of 10 N acts at a perpendicular distance of 2 m from a reference point. Its moment about that point is:
A.
5 N m
B.
12 N m
C.
20 N m
D.
0.2 N m
Correct Answer:
20 N m
Explanation:
The moment about the reference point is force multiplied by perpendicular distance: 10 N × 2 m = 20 N m.
5. The perpendicular distance used to calculate the moment of a force is measured from the reference point to the:
A.
Centre of mass
B.
Point of application only
C.
Line of action of the force
D.
Nearest edge of the body
Correct Answer:
Line of action of the force
Explanation:
Moment about a reference point equals the force multiplied by the perpendicular distance from that point to the force's line of action.
6. A force produces a clockwise moment about one reference point. About another reference point, its moment can be:
A.
Only clockwise
B.
Only zero
C.
Clockwise, anticlockwise, or zero
D.
Always equal to the force
Correct Answer:
Clockwise, anticlockwise, or zero
Explanation:
Changing the reference point can change the direction or magnitude of the moment, and the moment may even become zero.
7. For a force acting on a rigid body, the moment is taken about a reference point mainly to determine its:
A.
Rotational effect
B.
Temperature
C.
Mass density
D.
Volume
Correct Answer:
Rotational effect
Explanation:
The moment of a force about a reference point measures the tendency of the force to rotate the body about that point.
8. If a force acts at the reference point itself, the moment of the force about that point is:
A.
Maximum
B.
Zero
C.
Equal to the force
D.
Equal to twice the force
Correct Answer:
Zero
Explanation:
The perpendicular distance from the reference point to the line of action is zero when the force acts at that point.
9. A force of 5 N has a moment of 15 N m about a reference point. The perpendicular distance from the point to the force's line of action is:
A.
0.3 m
B.
3 m
C.
10 m
D.
75 m
Correct Answer:
3 m
Explanation:
Using moment = force × perpendicular distance, the distance is 15 N m ÷ 5 N = 3 m.
10. When selecting a reference point for calculating moments, a convenient choice is often a point:
A.
Through which an unknown force acts
B.
Farthest from all forces
C.
Outside the universe
D.
With the greatest mass
Correct Answer:
Through which an unknown force acts
Explanation:
Choosing a reference point on the line of action of an unknown force makes its moment zero, simplifying the calculation.
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