physics : class11 Zero Moment : Moment of a Force : Motion of System of Particles and Rigid Body MCQ Questions and Answers
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Zero Moment
MCQ questions and answers.
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MCQ Questions
1. The moment of a force about a point is zero when the line of action of the force
A.
passes through the point
B.
is farthest from the point
C.
is perpendicular to the position vector
D.
has the greatest magnitude
Correct Answer:
passes through the point
Explanation:
The moment of a force is force multiplied by the perpendicular distance from the point to its line of action. If the line of action passes through the point, this distance is zero, so the moment is zero.
2. A force of 10 N acts directly toward a pivot along the line joining the force application point to the pivot. What is its moment about the pivot?
A.
0 N m
B.
10 N m
C.
100 N m
D.
1 N m
Correct Answer:
0 N m
Explanation:
The force acts along the line joining its point of application to the pivot, so the perpendicular distance is zero. Therefore, its moment about the pivot is zero.
3. Which expression gives a zero moment of a force about a point when the force is nonzero?
A.
F multiplied by zero perpendicular distance
B.
F multiplied by maximum perpendicular distance
C.
F multiplied by a nonzero distance
D.
F divided by the perpendicular distance
Correct Answer:
F multiplied by zero perpendicular distance
Explanation:
The magnitude of moment is force multiplied by the perpendicular distance from the reference point to the force's line of action. A zero perpendicular distance gives a zero moment.
4. A force acts at the pivot itself. What is the moment of this force about the pivot?
A.
Zero
B.
Equal to the force
C.
Equal to twice the force
D.
Maximum
Correct Answer:
Zero
Explanation:
When the force acts at the pivot, its line of action passes through the pivot. Hence, the perpendicular distance is zero and the moment is zero.
5. For a force F acting at a position vector r from a point, the moment is zero when the angle between r and F is
A.
0 degrees
B.
45 degrees
C.
60 degrees
D.
90 degrees
Correct Answer:
0 degrees
Explanation:
The moment magnitude is rF sin(theta). When the angle is 0 degrees, sin(theta) is zero, so the moment is zero. The force and position vector are then along the same line.
6. A horizontal force acts along a straight rod, with the pivot at one end of the rod. What is the moment of the force about the pivot?
A.
Zero
B.
Equal to force times rod length
C.
Equal to force divided by rod length
D.
Maximum possible
Correct Answer:
Zero
Explanation:
The force acts along the rod, so its line of action passes through the pivot. Therefore, the perpendicular distance from the pivot to the line of action is zero.
7. If the perpendicular distance between a point and the line of action of a force is zero, the moment of the force about that point is
A.
Zero
B.
Negative
C.
Equal to the force magnitude
D.
Infinite
Correct Answer:
Zero
Explanation:
Moment equals the force magnitude multiplied by the perpendicular distance. With zero distance, the moment is zero.
8. A force acts along the same straight line as the position vector from a pivot to the point of application. The moment about the pivot is
A.
Zero
B.
Small but nonzero
C.
Maximum
D.
Equal to the square of the force
Correct Answer:
Zero
Explanation:
When the force and position vector are along the same line, the angle between them is 0 degrees or 180 degrees. In either case, the perpendicular component producing moment is zero.
9. Which situation produces zero moment about a specified point?
A.
A force whose line of action passes through the point
B.
A force acting perpendicular to a lever arm
C.
A force acting at the end of the longest lever arm
D.
A force with the greatest magnitude and nonzero distance
Correct Answer:
A force whose line of action passes through the point
Explanation:
A force produces zero moment about a point when its line of action passes through that point, because the perpendicular distance is zero.
10. A force of 5 N is applied to a body, and its perpendicular distance from the pivot is 0 m. What is the moment about the pivot?
A.
0 N m
B.
1 N m
C.
5 N m
D.
25 N m
Correct Answer:
0 N m
Explanation:
The moment is calculated as F multiplied by perpendicular distance. Thus, 5 N multiplied by 0 m gives a moment of 0 N m.
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