1. 1. What is a force?A push or pull on an object that can change its motion or shape. Measured in newton (N).
2. 2. Define mass.Mass is the quantity of matter in an object and a measure of inertia. Unit: kilogram (kg).
3. 3. What is weight?Weight is the gravitational force on a mass: W = m·g. Unit: newton (N).
4. 4. Distinguish mass and weight (one line).Mass is intrinsic (kg); weight is force due to gravity (N) and depends on g.
5. 5. What is inertia?Inertia is the tendency of a body to resist change in its state of motion; measured by mass.
6. 6. Define momentum.Momentum p = m·v; a vector quantity representing 'quantity of motion'.
7. 7. What is impulse?Impulse equals change in momentum: J = F·Δt = Δp; unit N·s.
8. 8. What is meant by net force?Net force is the vector sum of all forces on an object; it determines acceleration.

9. 9. State Newton's first law.A body remains at rest or moves uniformly in a straight line unless acted upon by a net external force (law of inertia).
10. 10. State Newton's second law.F_net = m·a — the net force on a body equals its mass times acceleration (vector relation).
11. 11. State Newton's third law.For every action there is an equal and opposite reaction; they act on different bodies.
12. 12. If net force on an object is zero what happens?Acceleration is zero; the object is either at rest or moves with constant velocity.
13. 13. How to apply F = m·a in 1D?Choose positive direction, sum forces algebraically, set F_net = m·a with sign for acceleration.
14. 14. Give a real-life example of Newton's first law.Passengers lurch forward when a bus abruptly stops — their bodies keep moving due to inertia.
15. 15. Give a real-life example of Newton's third law.When you walk, your foot pushes ground backward (action) and ground pushes you forward (reaction).
16. 16. Why do action and reaction forces not cancel?They act on different bodies, so they cannot cancel on the same object.
17. 17. What is equilibrium?A state where net force is zero; object is at rest or moves uniformly.
18. 18. How are mass and inertia related?Mass is the quantitative measure of inertia — greater mass means greater resistance to change in motion.

19. 19. Write the SI unit of acceleration.Meters per second squared (m/s²).
20. 20. A net force of 12 N acts on mass 3 kg. What is acceleration?a = F/m = 12 / 3 = 4 m/s².
21. 21. If acceleration is constant, what is the relation between force and mass?For same force, acceleration ∝ 1/m (a decreases with increasing mass).
22. 22. How to find resultant force when two forces act along same line?Add algebraically taking directions into account (vector sum): same direction add, opposite subtract.
23. 23. What does a negative value of acceleration indicate?Acceleration opposite to chosen positive direction (deceleration if velocity positive).
24. 24. If two equal forces act in opposite directions on a body, what is acceleration?Net force zero → acceleration zero (no change in motion).
25. 25. Why is direction important in forces?Forces are vectors; magnitude alone doesn't determine motion — direction decides resultant and acceleration direction.
26. 26. State an easy method to solve 1D force problems.Draw free-body diagram, choose axis, sum forces → F_net = m·a, solve for unknowns.
27. 27. A 5 kg box has acceleration 2 m/s². Find net applied force.F = m·a = 5×2 = 10 N.
28. 28. What is meant by resultant force?The single force which has the same effect as the combined action of all actual forces (vector sum).

29. 29. What is friction?A resistive force between surfaces in contact that opposes relative motion or tendency to move.
30. 30. Name two types of friction.Static friction (prevents start of motion) and kinetic (sliding) friction (opposes motion).
31. 31. Write formula for kinetic friction.f_k = μ_k · N, where N is normal reaction and μ_k is coefficient of kinetic friction.
32. 32. How does normal reaction affect friction?Frictional force is proportional to normal reaction; more normal force → larger friction.
33. 33. Which is usually greater: static or kinetic friction?Static friction is usually greater than kinetic friction (μ_s > μ_k).
34. 34. How can we reduce friction between two surfaces?Use lubrication, polishing, ball bearings, or reduce normal force where possible.

35. 35. Define momentum.Momentum p = m·v; vector quantity representing motion; unit kg·m/s.
36. 36. State impulse-momentum theorem.Impulse J = F·Δt equals change in momentum Δp: J = Δp.
37. 37. How does increasing impact time affect force?For same Δp, larger Δt decreases average force (F = Δp/Δt) — principle behind airbags.
38. 38. Is momentum conserved in collisions?Yes — total linear momentum of a closed system is conserved in collisions (if no external force).
39. 39. What is unit of impulse?N·s (newton-second), equivalent to kg·m/s.
40. 40. Why do helmets reduce head injuries?Helmets increase impact time Δt, reducing average force (F = Δp/Δt) on the head.

41. 41. Give an example of action–reaction in daily life.Walking: foot pushes ground backward (action); ground pushes foot forward (reaction).
42. 42. How does a rocket lift off (brief)?Rocket expels gas downward; reaction from gas pushes rocket upward (Newton III).
43. 43. When you sit on a chair, identify action–reaction pair.Action: your weight on chair (downward). Reaction: chair's normal force upward on you.
44. 44. Does reaction always oppose motion?Not necessarily — reaction is opposite to the action force, not always opposite to motion direction.
45. 45. Why does a gun recoil when fired?Expelled bullet (action) gains forward momentum; gun gets backward momentum (reaction) — recoil conserves momentum.
46. 46. Can action and reaction be forces of same type?Yes — they can both be gravitational, normal, thrust, etc., but act on different bodies.

47. 47. What is a free-body diagram?A sketch showing all forces acting on a single object — used to sum forces and apply F = m·a.
48. 48. List three steps to solve a force problem.1) Draw free-body diagram; 2) Choose axes and sign convention; 3) Write F_net = m·a and solve.
49. 49. How to handle inclined plane problems (brief)?Resolve weight into components parallel (mg sinθ) and perpendicular (mg cosθ) to plane; apply F = m·a along axes.
50. 50. Give one quick exam tip for this chapter.Always draw forces and state sign convention; keep SI units and show steps — examiners value method as well as answer.