#
Motion

####
NCERT Chapter Questions and Answers and other Q & A

**Q1: An object has moved through a distance. Can it have zero displacements? If yes, support your answer with an example.**

Answer: Yes an object can have zero displacements even though it has moved through a distance. It happens when the object moves back to its original position i.e. final position coincides with the starting position.

Example: Suppose an object travels from O to C and then comes back to its original position O.

Total distance traveled = actual path covered = OC + CO = 25 + 25 = 50m

Total displacement = shortest distance between final position and initial position = 0m

**Q2: What do you mean by a body in rest?**

Answer: A body is said to be at rest if it does not change its position with respect to a fixed point in its surroundings.

**Q3: Are motion and rest absolute or relative? Explain with an example.**

Answer: No these terms rest and motion are relative. For example, a person inside a car, carrying a ball in his hand will see the ball is at rest. While for another person, outside the car will see the ball is also moving.

**Q4: What is meant by scalars and vectors?**

Answer:

**Scalar Quantities**: Quantities that require magnitudes only to specify them are called scalar quantities or scalars. Mass, length, time, temperature, angle, area, speed, distance, volume and density are examples of scalar quantities.
**Vector Quantities**: Quantities that require both magnitudes and direction to specify them are called vector quantities or vectors. Displacement, velocity, force, momentum, weight etc. are examples of vectors.

**Q5: 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:

As shown in the figure, let us assume, that the farmer starts from A.

Given, that the length of each side = 10m

Distance covered in 1 lap = Perimeter of ABCD = 4 x 10 = 40m

Time is taken by farmer to cover 1 lap = the 40s

Speed of farmer = Distance

**÷** Time Taken for one lap = 40/40s = 1m/s

Distance covered by farmer in 2min 20 secs = Speed x Time = 1 x 140s = 140m

Number of laps covered = 140 ÷ 40 = 3.5 laps.

⇒ After the 140s, the farmer will be at position C (i.e. 3 and ½ laps).

Displacement = AC = (AB

^{2} + BC

^{2})

^{½} (applying Pythagoras theorem)

= (100+100)

^{½} = 10√2 = 10 x 1.414 =

**14.14m ** .... (answer)

Question: Can you find out displacement, if the farmer starts from the mid-point of AB?
**Note**: Displacement is a vector quantity that measures the shortest distance (straight line) between the starting point and ending point, not taking the actual path travelled into account.