Chapter 7: Motion Long Questions | science Class 9 CBSE

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Chapter 7: Motion Long Questions | science Class 9 CBSE | ByteNotes.in

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Question 1

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Q1. What is motion? Explain with examples how motion is relative.

• Motion is a change in position of an object with time.
• It is perceived relative to a reference point or origin.
• Example: Passengers in a moving bus see trees moving backward, but a person on the road sees the bus as moving.
• The same object can appear to be in motion to one observer and at rest to another.
• Motion can be detected directly (e.g., car moving) or indirectly (e.g., air inferred by rustling leaves).
• Hence, motion is relative and depends on the observer’s frame of reference.

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Question 2

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Q2. Distinguish between distance and displacement with suitable examples.

• Distance is the total path length travelled; displacement is the shortest distance from initial to final position.
• Distance is a scalar quantity; displacement is a vector quantity.
• Distance can never be negative; displacement can be zero, positive, or negative.
• Example: Moving from O to A and back to C covers 95 km distance but displacement is 35 km.
• If a person moves in a circle and comes back to the start, distance is full circumference but displacement is zero.
• Displacement gives direction; distance does not.
• Displacement ≤ distance always.

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Question 3

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Q3. Differentiate between uniform and non-uniform motion with examples.

• Uniform motion: Object covers equal distances in equal intervals of time.
• Non-uniform motion: Object covers unequal distances in equal intervals of time.
• Example of uniform motion: A car moving steadily at 40 km/h.
• Example of non-uniform motion: A person jogging in a park or vehicle in traffic.
• Uniform motion has constant speed; non-uniform has variable speed.
• Graphs for uniform motion are straight lines; for non-uniform motion, they are curved.
• Uniform motion is predictable; non-uniform is not.

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Question 4

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Q4. Define speed. What are its types? How is average speed calculated?

• Speed is the rate of change of distance with time.
• It is a scalar quantity with unit metre/second (m/s).
• Types of speed: Uniform speed and Non-uniform speed.
• Average speed = Total distance travelled / Total time taken.
• Example: If an object travels 32 m in 6 seconds, average speed = 5.33 m/s.
• Speed does not require direction for definition.
• Common units include m/s, km/h, and cm/s.

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Question 5

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Q5. What is velocity? How is it different from speed?

• Velocity is the speed of an object in a given direction.
• It is a vector quantity; direction is essential.
• Speed only indicates magnitude; velocity includes direction.
• If direction changes, velocity changes even if speed remains the same.
• Units of velocity are the same as speed (m/s).
• Velocity can be positive, negative, or zero based on direction.
• Average velocity = Total displacement / Total time taken.

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Question 6

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Q6. What is acceleration? Give its formula and explain its types.

• Acceleration is the rate of change of velocity with time.
• It is a vector quantity with SI unit m/s².
• Formula: a = (v – u)/t, where v = final velocity, u = initial velocity, t = time.
• Positive acceleration means increasing speed; negative means decreasing.
• Uniform acceleration: Velocity changes equally in equal time intervals.
• Non-uniform acceleration: Velocity changes irregularly with time.
• Example: Free fall is uniform acceleration; car in traffic shows non-uniform.

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Question 7

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Q7. Derive the three equations of motion for uniformly accelerated motion.

• First equation: v = u + at (relates velocity, acceleration, and time).
• Second equation: s = ut + ½ at² (relates distance, time, and acceleration).
• Third equation: v² – u² = 2as (relates velocity and distance).
• Where: u = initial velocity, v = final velocity, a = acceleration, t = time, s = distance.
• These equations are applicable when acceleration is constant.
• Derivations can be done algebraically or graphically.
• Widely used in solving motion-related numerical problems.

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Question 8

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Q8. Explain with an example the difference between average speed and average velocity.

• Average speed = Total distance / Total time.
• Average velocity = Total displacement / Total time.
• Example: Usha swims 180 m in a 90 m pool to and fro in 1 minute.
• Average speed = 180 m / 60 s = 3 m/s.
• Displacement = 0 m as she returns to the start point, so average velocity = 0 m/s.
• Average speed considers total path; velocity considers start and end points.
• They may differ in value depending on path.

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Question 9

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Q9. Describe the graphical representation of uniform and non-uniform motion.

• Distance-time graph for uniform motion is a straight line.
• Non-uniform motion has a curved distance-time graph.
• Slope of distance-time graph gives speed.
• Velocity-time graph for uniform motion is a straight line parallel to time axis.
• Velocity-time graph for uniformly accelerated motion is a straight sloped line.
• Area under velocity-time graph gives displacement.
• Graphs provide quick visual understanding of motion.

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Question 10

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Q10. How can velocity-time graphs help determine displacement and acceleration?

• The slope of a velocity-time graph gives acceleration.
• A steeper slope indicates higher acceleration.
• Area under the graph equals displacement.
• Uniform velocity shows a straight horizontal line.
• Uniform acceleration shows an inclined straight line.
• Area under a triangle in velocity-time graph gives distance: (½ × base × height).
• Used in analyzing motion without solving equations.

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Chapter 7: Motion | Long Questions

Q1. What is motion? Explain with examples how motion is relative.

Q2. Distinguish between distance and displacement with suitable examples.

Q3. Differentiate between uniform and non-uniform motion with examples.

Q4. Define speed. What are its types? How is average speed calculated?

Q5. What is velocity? How is it different from speed?

Q6. What is acceleration? Give its formula and explain its types.

Q7. Derive the three equations of motion for uniformly accelerated motion.

Q8. Explain with an example the difference between average speed and average velocity.

Q9. Describe the graphical representation of uniform and non-uniform motion.

Q10. How can velocity-time graphs help determine displacement and acceleration?

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