Chapter 1 — Laws of Motion: Multiple Choice Questions
Instructions: Each question carries 1 mark. Choose the best answer.
1. Inertia of an object is quantified by its ______.
Answer
(a) Momentum (b) Force (c) Mass (d) Acceleration
✅ Answer: (c) Mass
ExplanationInertia is the tendency of an object to resist any change in its state of rest or uniform motion. It is directly proportional to mass. A heavier object has more inertia and is harder to set in motion or stop.
2. If a net force of 50 N acts on a body of mass 5 kg, the acceleration produced is ______.
Answer
(a) 25 m/s² (b) 50 m/s² (c) 10 m/s² (d) 5 m/s²
✅ Answer: (c) 10 m/s²
ExplanationBy Newton's Second Law: F = ma a = F/m = 50/5 = 10 m/s²
3. The moment of a couple is called ______.
Answer
(a) Force (b) Torque (c) Momentum (d) Impulse
✅ Answer: (b) Torque
ExplanationA couple consists of two equal and opposite forces acting at different points on a body. The turning effect produced by a couple is called torque (or moment of the couple). Torque = Force × perpendicular distance between the forces
4. Newton's third law of motion is applicable ______.
Answer
(a) only for a body at rest (b) only for a body in motion (c) only for a body in equilibrium (d) always, for all bodies
✅ Answer: (d) always, for all bodies
ExplanationNewton's third law states that every action has an equal and opposite reaction. This applies at all times, whether bodies are at rest, in motion, or in equilibrium. There are no exceptions.
5. Impulse is equal to ______.
Answer
(a) rate of change of momentum (b) change in momentum (c) momentum of the body (d) rate of momentum
✅ Answer: (b) change in momentum
ExplanationImpulse = Force × time = change in momentum = mv − mu Note: Rate of change of momentum = Force (Newton's Second Law), not impulse.
6. Which of the following is the correct relation for Newton's Second Law of Motion?
Answer
(a) F = ma (b) F = m/a (c) F = a/m (d) F = m + a
✅ Answer: (a) F = ma
ExplanationNewton's Second Law: The net force acting on a body is equal to the product of its mass and the acceleration produced. F = ma, where F is in Newtons, m in kg, and a in m/s².
7. A body of mass 4 kg is moving with a velocity of 5 m/s. The momentum of the body is ______.
Answer
(a) 9 kg m/s (b) 1 kg m/s (c) 20 kg m/s (d) 0.8 kg m/s
✅ Answer: (c) 20 kg m/s
ExplanationMomentum (p) = mass × velocity = 4 × 5 = 20 kg m/s
8. The value of acceleration due to gravity at the surface of the Earth is approximately ______.
Answer
(a) 8.9 m/s² (b) 9.8 m/s² (c) 10.8 m/s² (d) 6.7 m/s²
✅ Answer: (b) 9.8 m/s²
ExplanationThe standard value of acceleration due to gravity (g) at Earth's surface is 9.8 m/s² (sometimes approximated as 10 m/s² for calculations). It varies slightly with altitude and latitude.
9. When a force acts on a body for a certain time, the product of force and time is called ______.
Answer
(a) Work (b) Power (c) Impulse (d) Momentum
✅ Answer: (c) Impulse
ExplanationImpulse = Force × Time = F × t. It represents the total effect of a force acting over a period of time. Unit: N·s or kg·m/s.
10. The force responsible for the revolution of the Earth around the Sun is ______.
Answer
(a) Magnetic force (b) Centripetal force (c) Frictional force (d) Electrostatic force
✅ Answer: (b) Centripetal force
ExplanationAny body moving in a circular path requires a force directed toward the centre of the circle — this is centripetal force. For the Earth orbiting the Sun, gravity provides this centripetal force.
Quick Revision — Key Concepts for MCQs
| Concept | Key Point |
|---|
| Inertia | Proportional to mass; resistance to change in motion |
| Newton's 1st Law | Body stays at rest/uniform motion unless acted upon by net force |
| Newton's 2nd Law | F = ma; net force = mass × acceleration |
| Newton's 3rd Law | Every action has equal and opposite reaction; always applicable |
| Momentum | p = mv; unit: kg m/s |
| Impulse | F × t = change in momentum = mv − mu |
| Torque | Turning effect of a force or couple |
| Centripetal force | Force directed toward centre for circular motion |
| g | 9.8 m/s² at Earth's surface |
Common MCQ Traps to Avoid
- Impulse vs Force: Force = rate of change of momentum; Impulse = change in momentum (not rate)
- Inertia vs Momentum: Inertia depends only on mass; momentum depends on both mass and velocity
- Newton's 3rd Law: Action and reaction act on different bodies — they never cancel each other
- Torque vs Moment: They are the same thing for a force about a point
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