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Motion
Physics IX : Complete NCERT Exercise Solutions
Get detailed NCERT Solutions for Class 9 Science Chapter 8: Motion. Understand concepts of distance, displacement, velocity, acceleration, and graphical representation of motion with step-by-step solved numerical problems and equations of motion.
Question 8.1
An object has moved through a distance. Can it have zero displacement? If yes, support your answer with an example.
Answer & Explanation:
Yes, an object can have zero displacement even if it has covered a certain distance.
Example: If a person walks around a circular track and returns to the starting point, the distance travelled is not zero but the displacement is zero because the initial and final positions are the same.
Example: If a person walks around a circular track and returns to the starting point, the distance travelled is not zero but the displacement is zero because the initial and final positions are the same.
Question 8.2
A farmer moves along the boundary of a square field of side 10 m in 40 s. What will be the magnitude of displacement of the farmer at the end of 2 minutes 20 seconds?
Answer & Explanation:
Time taken to complete one round = 40 s
Total time = 2 min 20 s = 140 s
Number of rounds completed = 140 ÷ 40 = 3.5 rounds
After 3.5 rounds, the farmer reaches the point diagonally opposite to the starting point.
Displacement = diagonal of square = √(10² + 10²) = 10√2 m
Total time = 2 min 20 s = 140 s
Number of rounds completed = 140 ÷ 40 = 3.5 rounds
After 3.5 rounds, the farmer reaches the point diagonally opposite to the starting point.
Displacement = diagonal of square = √(10² + 10²) = 10√2 m
Question 8.3
Which of the following is true for displacement?
Answer & Explanation:
Correct statement:
• The magnitude of displacement is always less than or equal to the distance travelled by an object.
• The magnitude of displacement is always less than or equal to the distance travelled by an object.
Question 8.4
Distinguish between speed and velocity.
Answer & Explanation:
Speed: Distance travelled per unit time; it is a scalar quantity and has only magnitude.
Velocity: Displacement per unit time; it is a vector quantity and has both magnitude and direction.
Velocity: Displacement per unit time; it is a vector quantity and has both magnitude and direction.
Question 8.5
Under what condition(s) is the magnitude of average velocity of an object equal to its average speed?
Answer & Explanation:
The magnitude of average velocity is equal to average speed when the object moves in a straight line without changing its direction.
Question 8.6
What does the odometer of an automobile measure?
Answer & Explanation:
An odometer measures the total distance travelled by an automobile.
Question 8.7
What does the path of an object look like when it is in uniform motion?
Answer & Explanation:
When an object is in uniform motion, it moves along a straight line and covers equal distances in equal intervals of time.
Question 8.8
What is the nature of the distance-time graph for uniform and non-uniform motion?
Answer & Explanation:
• For uniform motion, the distance-time graph is a straight line.
• For non-uniform motion, the distance-time graph is a curved line.
• For non-uniform motion, the distance-time graph is a curved line.
Question 8.9
What can you say about the motion of an object if its distance-time graph is a straight line parallel to the time axis?
Answer & Explanation:
If the distance-time graph is a straight line parallel to the time axis, the object is at rest because its distance does not change with time.
Question 8.10
A body is thrown vertically upwards. What is its velocity at the highest point?
Answer & Explanation:
At the highest point of its motion, the velocity of the body becomes zero because it momentarily comes to rest before falling down.
📘 Exam Preparation Tip:
Practice deriving and applying the three equations of motion. Learn to interpret and draw distance-time and velocity-time graphs. Focus on solving numerical problems on uniform and non-uniform acceleration.