# NCERT Solution class 7 Science Chapter-13

Chapter – 13    Motion and Time

Chapter Exercise

Page no. – ()

Q.1Classify the following as motion along a straight line, circular or oscillatory motion:-

1. Motion your hands while running.
2. Motion of a horse pulling a cart on a strait road.

iii. Motion of a child in a merry – go – round.

1. Motion of a child on a see – saw.
2. Motion of the hammer of an electric bell.
3. Motion of a train on a straight bridge.

Ans.1

1. Oscillator Motion.
2. Linear Motion.

iii. Circular Motion.

1. Oscillatory Motion.
2. Oscillatory Motion.
3. Linear Motion.

Q.2– Which of

the following are not correct?

1. The basic unit of a time is second.
2. Every object moves with a constant speed.

iii. Distancing between two cities are measuring in kilometer.

1. The time period the given pendulum is constant.
2. The speed of a train is expressed by m/h.

Ans.2The following statements are in correct:-

1. Every object moves with a constant speed.
2. The time period the given pendulum is constant.
3. The speed of a train is expressed by m/h.

Q.3– A simple pendulum takes 32 s to complete 20 oscillation. What is the period of pendulum.

Ans.3

• Total Number of The Oscillation –
• Total time taken to complete 20 Oscillation – 32 s.

Time Period = __Total time taken__

Number of oscillation

= __32__ = 1.6 s

20

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

Ans.4

• The distance between two stadium = 240 km.
• Total time taken = 4 hours

Speed = ­­__Distance__

Time

Speed = __240__ = 60

4

= 60 km/ h.

Q.5The odometer of a car reads 57321.0 km when the clock shows the time 08:30 AM. What is the distance moved by the 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.

Ans.5

• The Initial reading of the odometer =0.
• The Final reading of the odometer =0.

Formula,

= 57336 – 57321. 0 = 15 km.

• The car’s starting time = 8:30 AM
• The car’s stop time = 8:50 AM
• So, Total time taken = 20 minutes.
• Total Distance = 15 km.

Speed = ­­__Distance covered__

Time taken

= __15­­__ = 0.75

20

= 0.75 km/ min.

Now,

• 1 Hour = 60 Minutes.
• 20 minutes = _1_

3

Speed = __Distance covered__

Time taken

= __15­­__  = 45

1/3

= 45 km/ h.

Q.6Salma 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.

Ans.6

• Time Taken by Salma = 15 Minutes
• Speed of Cycle = 2 m/ s.
• Minute convert into second = 15 * 60

= 90 Sec.

Speed = __Distance Covered__

Time Taken

Distance = Speed * Time

Distance = 2 * 900 = 1800

1000 = 1

1800 = __1__ * 1800   = 1.8

1000

= 1.8 kms

Q.7– Show the shape of the distance – time graph for the motion in the following cases:

1. A car moving with a constant speed.
2. A car parked on a side road.

Ans.7i.-

ii.-

Q.8– Which of the following regulations is correct?

1. Speed = Distance * Time
2. Speed = __Distance__

Time

iii. Speed = __Time__

Distance

1. Speed = ______1_______

Distance * Time

Ans.8– ii. Speed = __Distance__

Time

Q.9– The basic unit of speed is:

1. km/ h
2. m/ min

iii. km/ h

1. m/ s

Ans.9iv. m/ s.

Q.10– A car moves with 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:-

1. 100 km
2. 25 km

iii. 15 km

1. 10 km

Ans.10ii. 25 km.

Q.11Suppose the two photographs, shown in fig. 13.1 and fig. 13.2 of NCERT 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 blue car.

Ans.11– Speed = 10 m/ s.

Q.12Fig 13.10 shows the distance – time graph for the motion of two vehicles A and B. Which one of them is moving faster?

Fig. 13.15 Distance – time graph for the motion of two cars

Ans.12The Car ‘A’ is moving fast.

Q.13Which of the following distance-time graphs shows a truck moving with speed which is not constant?

Ans.13– iii.