Dynamics is the branch of mechanics that studies the causes of motion. This chapter explains force, inertia, mass, weight, Newton’s laws of motion, momentum, and the effects of friction. It also discusses balanced and unbalanced forces, action-reaction pairs, and the relationship between force and acceleration. The MCQs below will help students test their understanding of these important principles.
1. Which law of motion explains the concept of inertia?
- A. Newton’s first law ✅
- B. Newton’s second law
- C. Newton’s third law
- D. Law of gravitation
Explanation: Newton’s first law states that an object continues in its state of rest or uniform motion unless acted upon by an external force.
2. The SI unit of force is:
- A. Newton ✅
- B. Joule
- C. Kilogram
- D. Watt
Explanation: One newton is the force required to accelerate 1 kg of mass by 1 m/s².
3. Which quantity measures the reluctance of a body to change its state of motion?
- A. Mass ✅
- B. Weight
- C. Force
- D. Velocity
Explanation: Mass is a measure of inertia — the resistance to change in motion.
4. According to Newton’s second law, force is equal to:
- A. Mass × acceleration ✅
- B. Mass × velocity
- C. Mass ÷ time
- D. Energy ÷ distance
Explanation: F = ma, where force is proportional to mass and acceleration.
5. Momentum is defined as:
- A. Mass × velocity ✅
- B. Force × distance
- C. Weight × acceleration
- D. Energy ÷ time
Explanation: Momentum (p) is a vector quantity given by p = mv.
6. Which law explains action and reaction forces?
- A. Newton’s third law ✅
- B. Newton’s first law
- C. Newton’s second law
- D. Law of conservation of momentum
Explanation: Newton’s third law states: For every action, there is an equal and opposite reaction.
7. The SI unit of momentum is:
- A. kg·m/s ✅
- B. m/s²
- C. Newton
- D. Joule
Explanation: Momentum has the unit kilogram meter per second.
8. Friction always acts:
- A. Opposite to the direction of motion ✅
- B. Along the direction of motion
- C. Perpendicular to motion
- D. In random directions
Explanation: Friction opposes relative motion between two surfaces in contact.
9. Which factor does NOT affect friction?
- A. Surface area in contact ✅
- B. Nature of surfaces
- C. Normal force
- D. Type of material
Explanation: Friction depends on surface texture and normal force, not on contact area.
10. Weight is the force due to:
- A. Gravity ✅
- B. Inertia
- C. Motion
- D. Friction
Explanation: Weight = mass × gravitational acceleration.
11. The unit of weight is the same as:
- A. Force ✅
- B. Mass
- C. Energy
- D. Power
Explanation: Weight is a force, so its unit is the newton.
12. A body at rest has:
- A. Zero velocity and zero acceleration ✅
- B. Zero velocity but non-zero acceleration
- C. Constant velocity
- D. Constant acceleration
Explanation: At rest, both velocity and acceleration are zero.
13. Which force prevents us from slipping while walking?
- A. Friction ✅
- B. Gravity
- C. Tension
- D. Normal force
Explanation: Friction between shoes and ground prevents slipping.
14. The momentum of a body is doubled if:
- A. Its velocity is doubled ✅
- B. Its mass is halved
- C. Its speed is halved
- D. Its direction is changed
Explanation: Since p = mv, doubling v doubles momentum.
15. Which principle is used in rocket propulsion?
- A. Newton’s third law ✅
- B. Newton’s first law
- C. Law of inertia
- D. Law of gravitation
Explanation: Rockets work on action-reaction forces.