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:
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.