Page No 102: - Chapter 8 - Motion - Ncert Solutions class 9 - Science
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Question 1:
Distinguish between speed and velocity.
Answer:
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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 interval 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 three values. |
Question 2:
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:
What does the odometer of an automobile measure?
Answer:
The odometer of an automobile measures the distance covered by an automobile.
Question 4:
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:
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, 3 × 108 m s−1.
Answer:
Time taken by the signal to reach the ground station from the spaceship
= 5 min = 5 × 60 = 300 s
Speed of the signal = 3 × 108 m/s
∴Distance travelled = Speed × Time taken = 3 × 108 × 300 = 9 × 1010 m
Hence, the distance of the spaceship from the ground station is 9 × 1010 m.
