NCERT Solutions for Class 7 Science Chapter 13 Motion and Time are part of NCERT Solutions for Class 7 Science. Here we have given NCERT Solutions for Class 7 Science Chapter 13 Motion and Time.

Board |
CBSE |

Textbook |
NCERT |

Class |
Class 7 |

Subject |
Science |

Chapter |
Chapter 13 |

Chapter Name |
Motion and Time |

Number of Questions Solved |
13 |

Category |
NCERT Solutions |

## NCERT Solutions for Class 7 Science Chapter 13 Motion and Time

**Question 1.**

Classify the following as motion along a straight line, circular or oscillatory motion:

- Motion of your hands while running.
- Motion of a horse pulling a cart on a straight road.
- Motion of a child in a merry-go-round.
- Motion of a child on a see-saw.
- Motion of the hammer of an electric bell.
- Motion of a train on a straight bridge.

**Answer:**

- Oscillatory
- Straight line
- Circular
- Oscillatory
- Oscillatory
- Straight line

**Question 2.**

Which of the following are not correct?

(i) The basic unit of time is second.

(ii) Every object moves at a constant speed.

(iii) Distance between two cities is measured in kilometers.

(iv) The time period of a given pendulum is not constant.

(v) The speed of a train is expressed in m/h.

**Answer:**

(ii), (iv), (v).

**Question 3.**

A simple pendulum takes 32 sec. to complete 20 oscillations. What is the time period of the pendulum?

**Answer:**

Time taken for 20 oscillations = 32 s

Time taken for 1 oscillation = \(\frac { 32 s }{ 20 } \)

Hence, Time period = 1.6 s

**Question 4.**

The distance between the two stations is 240 km. A train takes 4 hours to cover this distance. Calculate the speed of the train.

**Answer:**

Given, distance = 240 km

time = 4 h

speed = \(\frac { distance }{ time } \) = \(\frac { 240 km }{ 4 h } \) = 60 km/h.

**Question 5.**

The odometer of a car reads 57321.0 km when the clock shows the time 08: 30 AM. What is the distance moved by car, if at 08: 50 AM, the odometer reading has changed to 57336.0 km? Calculate the speed of the car in km/min during this time. Express the speed in km/h also.

**Answer:**

In this question, it is given that,

Initial reading of odometer = 57321.0 km

Final reading of odometer = 57336.0 km

Initial time = 08.30 AM

Final time = 08.50 AM

Now, total distance covered = Final reading of odometer – Initial reading of odometer

= 57336.0 km – 57321.0 km = 15.0 km

Total time taken = Final time – Initial time

= 08.50 AM – 08.30 AM

= 20 min

We know that,

speed = \(\frac { Distance\quad covered }{ Time\quad taken } =\frac { 15Km }{ 20min } =0.75Km/min\)

Speed in km/h = 0.75 x 60 (1 hr = 60 min) = 45 km/hr

Therefore, the distance moved by the car =15 km

and the speed of the car = 0.75 km/min and 45 km/h.

**Question 6.**

Salma takes 15 minutes from her house to reach her school on a bicycle. If the bicycle has a speed of 2 m/s, calculate the distance between her house and the school.

**Answer:**

Given, Speed = 2 m/s

Time =15 min = 15 x 60 s = 900 s

distance = speed x time = 2 m/s x 900 s = 1800 m

\(\frac { 1800 m }{ 1000 } \) km = 1.8 km

**Question 7.**

Show the shape of the distance-time graph for the motion in the following cases:

(i) A car moving at a constant speed.

(ii) A car parked on a side road.

**Answer:**

**Question 8.**

Which of the following relations is correct?

(i) Speed = Distance × Time

(ii) Speed = \(\frac { Distance }{ Time }\)

(iii) Speed = \(\frac { Time }{ Distance }\)

(iv) Speed = \(\frac { 1 }{ Distance\times Time } \)

**Answer:**

**(ii)** Speed = \(\frac { Distance }{ Time }\)

**Question 9.**

The basic unit of speed is:

(i) km/min

(ii) m/min

(iii) km/h

(iv) m/s

**Answer:**

**(iv)** m/s

**Question 10.**

A car moves with a speed of 40 km/h for 15 minutes and then with a speed of 60 km/h for the next 15 minutes. The total distance covered by the car is:

(i) 100 km

(ii) 25 km

(iii) 15 km

(iv) 10 km

**Answer:**

**(ii)** 25 km

**Question 11.**

Suppose the two photographs shown in Figures A and B 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 red car.

**Answer:**

Do it yourself.

**Question 12.**

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

Fig. Distance-time graph for the motion of two cars

**Answer:**

A is moving faster.

**Question 13.**

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

**Answer:**

**(ii)** and **(iii).**

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