NCERT Class 9 Science Solutions: Chapter 8 – Motion Part 2

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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:

Table Contains Shows Distinguish between Speed and Velocity for Motion
Table contains shows Distinguish between Speed and Velocity for Motion

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.

Q 1 Image Showing Speed V/S Velocity.

Q 1 Image Showing Speed V/S Velocity

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.

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