# NCERT Class 9 Science Solutions: Chapter 8 – Motion Part 2 (For CBSE, ICSE, IAS, NET, NRA 2022)

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Question 1:

Q. An artificial satellite is moving in a circular orbit of radius 42250 km. Calculate its speed if it takes 25 hours to revolve around the earth?

**Answer**:

Radius of the circular orbit,

Time taken to revolve around the earth,

Speed of a circular moving object,

Hence, the speed of the artificial satellite is 3.069 km/s.

Question 1:

Q. Distinguish between speed and velocity.

**Answer**:

Speed | Velocity |

Speed is the distance travelled by an object in a given interval of time. It does not have any direction. | Velocity is the displacement of an object in a given internal of time. It has a unique direction. |

Speed is given by the relation: | Velocity is given by the relation: |

The speed of an object can never be negative. At the most, it can become zero. This is because distance travelled can never be negative. | The velocity of an object can be negative, positive, or equal to zero. This is because displacement can take any of these tree value. |

Question 2:

Q. Under what condition (s) is the magnitude of average velocity of an object equal to its average speed?

**Answer**:

If the total distance covered by an object is the same as its displacement, then its average speed would be equal to its average velocity.

Question 3:

Q. What does the odometer of an automobile measure?

**Answer**:

The odometer of an automobile measure the distance covered by an automobile.

Question 4:

Q. What does the path of an object look like when it is in uniform motion?

**Answer**:

An object having uniform motion has a straight line path.

Question 5:

Q. During an experiment, a signal from a spaceship reached the ground station in five minutes. What was the distance of the spaceship from the ground station? The signal travels at the speed of light, that is, .

**Answer**:

Time taken by the signal to reach the ground station from the spaceship

Speed of the signal

Hence, the distance of the spaceship from the ground station is .

Question 1:

Q. When will you say a body is in (i) uniform acceleration? (ii) Non-uniform acceleration?

**Answer**:

(i) A body is said to have uniform acceleration if it travels in a straight path in such a way that its velocity changes at a uniform rate, i.e.. , the velocity of a body increase or decrease by equal amounts in an equal interval of time.

(ii) A body is said to have non-uniform acceleration if it travels in a straight path in such a way that its velocity changes at a non-uniform rate, i.e.. , the velocity of a body increases or decreases in unequal amounts in an equal interval of time.