The turning effect of forces, also called the moment of force, describes how forces cause objects to rotate. This chapter explains torque, the principle of moments, center of mass, types of equilibrium, and applications of levers. It also covers how couples work and the factors affecting rotational stability. The MCQs below will help students test their understanding of rotational mechanics and related concepts.
1. The turning effect of a force about a point is called:
- A. Moment of force ✅
- B. Torque
- C. Inertia
- D. Impulse
Explanation: Moment of force is the product of force and its perpendicular distance from the pivot point.
2. The SI unit of moment of force is:
- A. Newton meter ✅
- B. Newton second
- C. Joule
- D. Watt
Explanation: Moment of force is measured in newton meters (N·m).
3. Torque is defined as:
- A. Force × perpendicular distance from pivot ✅
- B. Mass × acceleration
- C. Force ÷ distance
- D. Weight × height
Explanation: Torque measures the tendency of a force to cause rotation.
4. The principle of moments states that:
- A. Clockwise moments = anticlockwise moments in equilibrium ✅
- B. Force = mass × acceleration
- C. Momentum is conserved
- D. Energy cannot be created or destroyed
Explanation: For rotational equilibrium, total clockwise moment equals total anticlockwise moment.
5. The point where the entire weight of a body appears to act is called:
- A. Center of mass ✅
- B. Pivot
- C. Axis of rotation
- D. Torque point
Explanation: The center of mass is the point of balanced mass distribution.
6. Which type of lever has the fulcrum between the load and the effort?
- A. First-class lever ✅
- B. Second-class lever
- C. Third-class lever
- D. None of these
Explanation: In first-class levers, the fulcrum is between load and effort (e.g., seesaw).
7. A seesaw is an example of:
- A. First-class lever ✅
- B. Second-class lever
- C. Third-class lever
- D. Inclined plane
Explanation: A seesaw has the pivot between effort and load.
8. Which lever has the load between the fulcrum and the effort?
- A. Second-class lever ✅
- B. First-class lever
- C. Third-class lever
- D. None
Explanation: Second-class levers provide mechanical advantage (e.g., wheelbarrow).
9. A fishing rod is an example of:
- A. Third-class lever ✅
- B. First-class lever
- C. Second-class lever
- D. None
Explanation: In a third-class lever, the effort is applied between the fulcrum and load.
10. A couple is a pair of forces which are:
- A. Equal, opposite, and parallel ✅
- B. Equal, opposite, and perpendicular
- C. Unequal and opposite
- D. Equal and in the same direction
Explanation: A couple causes rotation without translation.
11. The SI unit of torque is the same as:
- A. Work ✅
- B. Power
- C. Momentum
- D. Pressure
Explanation: Torque and work share the same unit (N·m), but they are different physical quantities.
12. Which factor does NOT affect the stability of an object?
- A. Color of the object ✅
- B. Height of center of mass
- C. Size of base
- D. Weight distribution
Explanation: Stability depends on center of mass and base area, not color.
13. The moment of a force increases if:
- A. Perpendicular distance from pivot increases ✅
- B. Force decreases
- C. Pivot is moved closer
- D. Force acts at pivot
Explanation: Greater distance from pivot increases the turning effect.
14. When the total clockwise moment equals the total anticlockwise moment, the body is in:
- A. Rotational equilibrium ✅
- B. Translational motion
- C. Acceleration
- D. Free fall
Explanation: This is the condition for rotational equilibrium.
15. Which device works on the principle of moments?
- A. Beam balance ✅
- B. Spring balance
- C. Thermometer
- D. Stopwatch
Explanation: Beam balances use moments to compare weights.