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NCERT · Class 9 · Science

Chapter 7: Motion

Practice each question, then open the answer or worked solution.

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Intext Questions – 2

Textbook page 102 · 5 questions
Q1Written answer

Distinguish between speed and velocity.

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Worked solution
Difference Between Speed and Velocity
Velocity Speed
Velocity can be defined as the rate at which an object changes position in a certain direction The rate at which an object covers a certain distance is known as speed
The velocity of the object changes with the change in direction, therefore the object must follow one direction The average speed will continue to count even if the object changes direction
Vector quantity Scalar quantity
Velocity can be zero, negative, or positive Speed can never be negative or zero
Q2Written answer

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

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Worked solution

Since average speed is the total distance travelled in a time frame and velocity is the total displacement in the time frame, the magnitude of average velocity and average speed will be the same when the total distance travelled is equal to the displacement.

Q3Written answer

What does the odometer of an automobile measure?

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Worked solution

An odometer, or odograph, is a device that measures the distance travelled by an automobile based on the perimeter of the wheel as the wheel rotates.

Q4Written answer

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

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Worked solution

The path of an object in uniform motion is a straight line.

Q5Written answer

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.

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Worked solution

Given that the signal travels in a straight line, the distance between the spaceship and the ground station is equal to the total distance travelled by the signal.

5 minutes = 5*60 seconds = 300 seconds.

Speed of the signal = 3 × 108 m/s.

Therefore, total distance = (3 × 108 m/s) * 300s

= 9*1010 meters.