🔹 Very Short Answer (1 mark)
Q1. Define force.
Ans. A push or pull on an object which can change its state of rest or motion.
Q2. What is the SI unit of force?
Ans. Newton (N).
Q3. Who formulated the three laws of motion?
Ans. Sir Isaac Newton.
Q4. Define inertia.
Ans. The tendency of a body to resist any change in its state of motion or rest.
Q5. What is mass?
Ans. The measure of inertia of a body.
Q6. Give formula connecting force, mass and acceleration.
Ans. F = ma.
Q7. What is momentum?
Ans. Momentum (p) is the product of mass and velocity of a body: p = mv.
Q8. What is the unit of momentum?
Ans. kg·m/s.
Q9. What is a balanced force?
Ans. Equal and opposite forces acting on a body that do not change its motion.
Q10. What is an unbalanced force?
Ans. A force that changes the state of motion of a body.
🔹 Short Answer (2–3 marks)
Q11. State Newton’s first law of motion.
Ans. A body at rest remains at rest, and a body in motion continues in motion at the same velocity unless acted upon by an unbalanced external force.
Q12. Give an example of inertia of rest.
Ans. A book on a table remains at rest until someone pushes it.
Q13. Give an example of inertia of motion.
Ans. A moving car continues moving when brakes are suddenly applied.
Q14. Give an example of inertia of direction.
Ans. A stone tied to a string moves tangentially when string is released during circular motion.
Q15. State Newton’s second law of motion.
Ans. The rate of change of momentum of a body is directly proportional to the applied force and takes place in the direction of the force. (F = ma)
Q16. State Newton’s third law of motion.
Ans. For every action, there is an equal and opposite reaction.
Q17. Give one example of Newton’s third law.
Ans. When we sit on a chair, our body exerts force on the chair and the chair exerts equal and opposite force on our body.
Q18. Define gravitational force.
Ans. The attractive force acting between any two objects due to their masses.
Q19. Give one example of frictional force.
Ans. The force resisting motion when a book slides on a table.
Q20. Give one method to reduce friction.
Ans. Use of lubricants like oil, grease.
🔹 Long Answer (4–5 marks)
Q21. Differentiate between mass and weight.
| Mass | Weight |
|---|---|
| Measure of matter in body | Force due to gravity on body |
| Unit: kg | Unit: N |
| Scalar quantity | Vector quantity |
| Constant | Varies with g |
Q22. Differentiate between balanced and unbalanced forces.
| Balanced Force | Unbalanced Force |
|---|---|
| No change in motion | Changes motion |
| Equal magnitude, opposite | Unequal or net force present |
Q23. What is the relation between force and acceleration?
Ans. Acceleration produced in a body is directly proportional to applied force and inversely proportional to mass. F = ma.
Q24. Explain the importance of Newton’s first law of motion.
Ans.
- Explains concept of inertia.
- Describes that force is needed to change the state of motion.
- Helps in designing safety features like seat belts.
Q25. Explain the importance of Newton’s second law.
Ans.
- Quantitatively connects force, mass, and acceleration.
- Helps calculate required force to move objects.
Q26. Explain the importance of Newton’s third law.
Ans.
- Explains action-reaction in walking, swimming, rocket propulsion.
Q27. What is rolling friction?
Ans. Friction between a rolling object and surface. Less than sliding friction.
Q28. Differentiate between static and kinetic friction.
| Static Friction | Kinetic Friction |
|---|---|
| Acts on stationary objects | Acts on moving objects |
| Prevents motion | Opposes motion |
Q29. How does mass affect inertia?
Ans. Greater the mass, greater the inertia; heavier objects resist changes in motion more.
Q30. Define momentum and state its law of conservation.
Ans. Total momentum of an isolated system remains constant if no external force acts on it.
🔹 Case Study / Application-Based (5–6 marks)
Q31. Case Study – Rocket Propulsion
A rocket moves upward by expelling gas downward.
(i) Which law of motion is demonstrated?
(ii) Explain.
Ans.
(i) Newton’s third law.
(ii) Action: gas moves downward, Reaction: rocket moves upward.
Q32. Case Study – Seat Belts
Seat belts prevent passengers from hitting the dashboard.
(i) Which concept is applied?
(ii) Explain.
Ans.
(i) Newton’s first law (inertia of motion).
(ii) When car stops suddenly, inertia tries to keep passengers moving; seat belt exerts force to stop them safely.
Q33. Why does a tablecloth pull-out trick work?
Ans. Inertia of rest keeps dishes on table stationary while cloth is pulled quickly.
Q34. A book is sliding on table and comes to rest. Why?
Ans. Due to unbalanced frictional force acting opposite to motion.
Q35. Case Study – Moving Bus
When bus accelerates, passengers fall backward; when brakes, they fall forward.
Ans. Due to inertia of motion resisting sudden change in velocity.
Q36. Why do rockets move in space even though no air?
Ans. Newton’s third law: expulsion of gas produces equal and opposite reaction.
Q37. Why is friction sometimes useful?
Ans.
- Helps in walking, writing, car brakes, holding objects.
Q38. Why is friction sometimes disadvantageous?
Ans.
- Causes wear and tear, heat, energy loss.
Q39. How does lubrication reduce friction?
Ans. Forms a thin layer between surfaces reducing direct contact.
Q40. A person jumps from a boat to shore. Why does boat move backward?
Ans. Newton’s third law – action: person moves forward, reaction: boat moves backward.
🔹 Extra Important (41–50)
Q41. Define net force.
Ans. The vector sum of all forces acting on a body.
Q42. Define equilibrium.
Ans. When net force on a body is zero, body is in equilibrium.
Q43. Differentiate between linear and circular motion.
| Linear Motion | Circular Motion |
|---|---|
| Moves along a straight line | Moves along a circular path |
| Acceleration may vary | Centripetal acceleration present |
Q44. What is centripetal force?
Ans. Force directed towards center keeping a body in circular motion.
Q45. Give example of action-reaction pairs.
Ans.
- Walking → foot pushes ground backward, ground pushes foot forward.
- Swimming → hand pushes water backward, water pushes hand forward.
Q46. Why do heavier bodies need more force to move?
Ans. Greater mass → greater inertia → more force needed (F = ma).
Q47. Why do we apply brakes to stop moving vehicles?
Ans. To produce unbalanced force opposite to motion → deceleration.
Q48. What happens when two equal and opposite forces act on a body?
Ans. Body remains in same state of motion (balanced forces).
Q49. How is momentum conserved in collision?
Ans. Total momentum before collision = total momentum after collision (if no external force acts).
Q50. Why do wheels of vehicles reduce friction?
Ans. Rolling friction is less than sliding friction → easier movement.