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NCERT · Class 7 · Science

Chapter 9: Motion and Time

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

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Questions

13 questions
Q11Written answer

Suppose the two photographs, shown in Fig. 13.1 and Fig. 13.2, had been taken at an interval of 10 seconds. If a distance of 100 metres is shown by 1 cm in these photographs, calculate the speed of the fastest car.

Speed calculation

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Worked solution

The distance covered by the blue car (as evident from the photograph) from one horizontal white strip to another, which is measured by scale is 1.2 cm.

It is given that 1 cm is equivalent to 100 m.

Therefore, 1.2 cm is equivalent to 120 m.

Distance travelled by the car = 120 m

Time taken to cover this distance = Time interval between the two photographs = 10 s

Speed formula

= 120/10

= 12 m/s

Q12Written answer

Fig. 13.15 shows the distance-time graph for the motion of two vehicles A and B. Which one of them is moving faster?

Distance time graph

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Worked solution

Vehicle A is moving faster than vehicle B.

Q13Written answer

Which of the following distance-time graphs shows a truck moving with speed which is not constant?

Distance time graph
Distance time graph

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Worked solution

Answer is iii)

Introduction to NCERT Solutions Class 7 Science Motion and Time:

Class 7 NCERT Chapter 13 is an important chapter of physics that deals with the fundamentals of speed, including types and calculation of speed and motion. This chapter gives information on uses of speed and motion in our daily life. It includes a real-life demonstration which will motivate students to learn the topic with curiosity and interest.

The Central Board of Secondary Education is one of the popular educational boards in India. The NCERT Solutions Class 7 Science Motion and Time are provided so that students can understand the concepts of this chapter in-depth and resolve their doubts.

NCERT Class 7 Science Chapter 13 Revision Notes

The smallest time interval that can be measured with commonly available clocks and watches is one second. Some key points to remember from the chapter are given below.

  • Speed of objects helps us to decide which one is moving faster than the other.
  • The distance moved by an object in a unit time is called its speed.
  • The speed of an object is the distance travelled divided by the time taken to cover that distance. Its basic unit is metre per second (m/s).
  • The motion of objects can be presented in pictorial form by their distance-time graphs.
  • Periodic events are used for the measurement of time. The periodic motion of a pendulum has been used to make clocks and watches.
  • The distance-time graph for the motion of an object moving with a constant speed in a straight line.
  • Graph of distance and time for the  motion of an object with constant speed will be a straight line
Important topics covered in NCERT Solutions for Class 7 Science Chapter 13 Motion and Time
  1. Slow/Fast – The distance moved by objects in a given interval of time can help us to decide which one is faster or slower
  2. Speed – Can define the distance covered by an object in unit time as the speed of the object.
  3. Measurement of time
  4. Measurement of speed
  5. Distance-time graph

For all the chapters of NCERT Solutions for Class 7 Science, visit BYJU’S. You can also download Class 7 Science exemplar problems, worksheets, e-books as well as previous year solved question papers.