Basics & Definitions (Q1–Q10)
Q1. What is motion?
A change in the position of an object with respect to time and a reference point.
Q2. Define distance.
Total length of the path travelled by an object; it is a scalar quantity.
Q3. Define displacement.
Shortest straight-line distance from initial to final position, including direction; a vector.
Q4. Give one example where distance ≠ displacement.
Walking 3 m east then 3 m west: distance = 6 m, displacement = 0 m.
Q5. What is speed?
Rate of change of distance with time; scalar; SI unit m/s.
Q6. What is velocity?
Rate of change of displacement with time; vector; includes direction and magnitude.
Q7. What is acceleration?
Rate of change of velocity with time; measured in m/s². Positive if speed increases in chosen positive direction.
Q8. Differentiate average speed and average velocity in one line.
Average speed = total distance/total time; average velocity = total displacement/total time.
Q9. What is instantaneous velocity?
Velocity of an object at a particular instant; obtained from the slope of tangent on s–t graph at that instant.
Q10. Can instantaneous speed be negative?
No — speed is scalar (non-negative); instantaneous velocity can be negative if direction is opposite to positive direction chosen.
Types of Motion (Q11–Q16)
Q11. What is uniform motion?
Motion with constant speed; displacement increases linearly with time if direction is unchanged.
Q12. What is non-uniform motion?
Motion in which speed or direction (hence velocity) changes with time.
Q13. What is uniformly accelerated motion?
Motion in which acceleration is constant in magnitude and direction throughout the time interval.
Q14. Provide an example of uniformly accelerated motion.
A car starting from rest and accelerating uniformly along a straight road with constant throttle.
Q15. Is circular motion covered in Class 9 Motion chapter?
Only an introductory concept is mentioned; detailed circular motion is usually in higher classes.
Q16. Can speed remain constant while velocity changes?
Yes — e.g., motion in a circle at constant speed: direction changes so velocity changes.
Units & Conversions (Q17–Q20)
Q17. SI unit of velocity?
Metre per second (m/s).
Q18. SI unit of acceleration?
Metre per second squared (m/s²).
Q19. Convert 72 km/h to m/s.
72 ÷ 3.6 = 20 m/s.
Q20. How to convert km/h into m/s (formula)?
Multiply by 5/18 (or divide by 3.6): v(m/s) = v(km/h) × 5/18.
Equations of Motion (Q21–Q30)
Q21. State the first equation of motion.
v = u + a t (v: final velocity, u: initial velocity, a: acceleration, t: time).
Q22. State the second equation of motion.
s = u t + ½ a t² (s: displacement in time t).
Q23. State the third equation of motion.
v² = u² + 2 a s (relates velocities, acceleration and displacement).
Q24. When is s = ½ a t² applicable?
When initial velocity u = 0 (motion starting from rest) with constant acceleration.
Q25. Which equation would you use when time is not given?
v² = u² + 2 a s (it eliminates the time variable).
Q26. If u = 0 and a = g for free fall, what is v after time t?
v = gt (taking downward positive), where g ≈ 9.8 m/s².
Q27. How is average velocity over an interval defined?
Average velocity = (displacement)/(time interval).
Q28. How do you choose which equation of motion to use?
Identify known quantities (u, v, a, s, t) and pick the equation that contains the unknown and known variables.
Q29. What physical quantity does 'a' represent in the equations?
'a' represents constant acceleration (rate of change of velocity).
Q30. Units check: what are units of ut and ½at² in s = ut + ½at²?
Both have units of metres (m): ut → (m/s)×s = m; ½at² → (m/s²)×s² = m.
Graphical Interpretation (Q31–Q36)
Q31. What does slope of s–t (distance–time) graph represent?
Slope of s–t graph represents speed (or velocity if s is displacement).
Q32. What does slope of v–t (velocity–time) graph represent?
Slope of v–t graph represents acceleration.
Q33. What does area under v–t graph give?
Area under v–t graph between two times gives the displacement in that time interval.
Q34. What does a horizontal line on v–t graph indicate?
Constant velocity (acceleration = 0).
Q35. How to obtain instantaneous velocity from s–t graph?
Draw a tangent to the s–t curve at the point and find its slope (Δs/Δt as Δt → 0).
Q36. On a v–t graph, what does a triangular area represent?
Triangular area usually represents displacement when velocity changes linearly (area = ½ × base × height).
Free Fall & Gravity (Q37–Q40)
Q37. What is free fall?
Motion of an object under the influence of gravity alone, neglecting air resistance.
Q38. Approximate value of acceleration due to gravity g?
Approximately 9.8 m/s² (often approximated to 10 m/s² for simple calculations).
Q39. For an object thrown vertically upward, what is acceleration during its ascent?
Acceleration is downward with magnitude g (negative if upward is taken positive), so it decelerates.
Q40. If a body is dropped from rest, which equation gives distance after time t?
s = ½ g t² (with u = 0 and a = g downward).
Relative Motion & Practical Questions (Q41–Q46)
Q41. Define relative velocity of A with respect to B.
vA/B = vA − vB (vector difference); velocity of A as seen from B.
Q42. How to find relative speed when two objects move towards each other?
Relative speed = sum of their speeds (vA + vB) if moving in opposite directions along a line.
Q43. A train moves at 72 km/h and a person walks inside it at 5 km/h in same direction. Ground speed of person?
Convert if needed or add speeds: 72 + 5 = 77 km/h relative to ground.
Q44. Why do we use sign convention in motion problems?
To assign positive/negative directions, keep calculations consistent for velocity and acceleration signs.
Q45. How to convert 20 m/s into km/h?
Multiply by 3.6: 20 × 3.6 = 72 km/h.
Q46. Give one use of motion graphs in real life.
Speed–time graphs are used in vehicle testing to analyse acceleration and braking performance.
Problem Solving & Short Numericals (Q47–Q50)
Q47. A car starts from rest and accelerates uniformly at 1.5 m/s² for 10 s. What is its final velocity?
v = u + at = 0 + 1.5×10 = 15 m/s.
Q48. A runner moves at 5 m/s for 20 s. How far does he run?
Distance = speed × time = 5 × 20 = 100 m (if motion is with constant speed).
Q49. A body has u = 10 m/s, v = 0 after 5 s. What is acceleration?
a = (v − u)/t = (0 − 10)/5 = −2 m/s² (deceleration of 2 m/s²).
Q50. A car covers 200 m in 10 s starting from rest with constant acceleration. What is acceleration?
Use s = ut + ½at² → 200 = 0 + 0.5 a (10²) → 200 = 50 a → a = 4 m/s².