Motion

NCERT In Text Solution

Question 1: An object has moved through a distance. Can it have zero displacement? If yes, support your answer with an example.

Answer: Yes, zero displacement is possible if an object has moved through a distance.

Class 9 Motion InText1

Suppose a ball starts moving from point A and it returns back at same point A, then the distance will be equal to 20 meters while displacement will be zero.


Question 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 from his initial position?

Answer:

Class 9 Motion InText2

Given, side of the square field = 10m

Therefore, perimeter = 10 m x 4 = 40 m

Farmer moves along the boundary in 40s.

Displacement after 2 m 20 s = 2 x 60 s + 20 s = 140 s =?

Since in 40 s farmer moves 40 m

∴ in 1s distance covered by farmer `= 40/40 m = 1m`

∴ in 140s distance covered by farmer `= 1xx 140m = 140m`


Now, number of rotation to cover 140m along the boundry` =text{Total distance}/text{Perimeter}`

`(140\ m)/(40\ m) = 3.5` round

Thus, after 3.5 round farmer will at point C of the field.

∴ Displacement `AC = sqrt((10m)^2+(10m)^2)`

`= sqrt(100m^2+100m^2)`

`= sqrt(200m^2)`

`=sqrt(2xx100m^2)`

`=10sqrt2 m`


Question 3: 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: None

Question 4: Distinguish between speed and velocity.

Answer: Speed has only magnitude while velocity has both magnitude and direction.

Question 5: Under what condition(s) is the magnitude of average velocity of an object equal to its average speed?

Answer: When distance is equal to displacement.

Question 6: What does the odometer of an automobile measure?

Answer: In automobiles, odometer is used to measure the distance.

Question 7: What does the path of an object look like when it is in uniform motion?

Answer: In the case of uniform motion the path of an object will look like a straight line.



Copyright © excellup 2014