NCERT Class 9 Science Solutions: Chapter 8 – Motion Part 1

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Question 1:

Q. An object has moved through a distance. Can it have zero displacement? If yes, support your answer with an example.

Answer:

Yes. AN object that has moved through a distance can have zero displacement. Displacement is the shortest measurable distance between the initial and the final position of an object. An object which has covered a distance can have zero displacement, if it comes back to its starting point, i.e., the initial position.

Consider the following situation. A man is walking in a square park of length 20 m (as shown in the following figure). He starts walking from point A and after moving along all the corners of the park (point B, C, D), he again comes back to the same point, i.e., A.

Image of the Path of Man Walking from a and After Moving Along All the Corners of the Park (Point B, C, D), He Again Comes Back to the Same Point.

Image of The Path of Man Walking from A and after moving along all the corners of the park (point B, C, D), he again comes back to the same point.

In this case, the total distance covered by the man is . However, his displacement is zero because the shortest distance between his initial and final position is zero.

Question 2:

Q. A farmer moves along the boundary of a square field of side in 40 s. What will be the magnitude of displacement of the farmer at the end of 2 minutes 20 seconds?

Answer:

The farmer takes to cover .

In and , he will cover a distance

Therefore, the farmer completes rounds of the field in 2 min and 20 s.

That means, after 2 min 20 s, the farmer will be at the opposite and of the starting point.

Now, there can be two extreme cases.

Q 2 (I) Question For Completes Rounds.

Q 2 (I) Question for Completes Rounds.

Q 2 (I) Question For Completes Rounds.

Case I: Starting point is a corner point of the field.

In this case, the farmer will be at the diagonally opposite corner of the field after 2 min 20 s.

Therefore, the displacement will be equal to the diagonal of the field.

Hence, the displacement will be

Case II: starting point is the middle point of any side of the field.

In this case the farmer will be at the middle point of the opposite side of the field after 2 min 20 s.

Therefore, the displacement will be equal to the side of the field, i.e., 10 m.

For any other starting point, the displacement will be between 14.1 m and 10 m.

Q 2 (II) Question For Displacement.

Q 2 (II) Question for Displacement.

Q 2 (II) Question For Displacement.

Question 3:

Q. Which of the following is true for displacement?

(a) It cannot be zero.

(b) Its magnitude is greater than the distance travelled by the object.

Answer:

(a) Not True

Displacement can become zero when the initial and final position of the object is the same.

(b) Not True

Displacement is the shortest measurable distance the initial and final positions of an object. It cannot be greater than the magnitude of the distance travelled by an object. However, sometimes, it may be equal to the distance travelled by the object.