NCERT Solution class 7 Science Chapter-13
Chapter – 13 Motion and Time
Chapter Exercise
Page no. – ()
Q.1– Classify the following as motion along a straight line, circular or oscillatory motion:-
- Motion your hands while running.
- Motion of a horse pulling a cart on a strait road.
iii. 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.
Ans.1–
- Oscillator Motion.
- Linear Motion.
iii. Circular Motion.
- Oscillatory Motion.
- Oscillatory Motion.
- Linear Motion.
Q.2– Which of the following are not correct?
- The basic unit of a time is second.
- Every object moves with a constant speed.
iii. Distancing between two cities are measuring in kilometer.
- The time period the given pendulum is constant.
- The speed of a train is expressed by m/h.
Ans.2– The following statements are in correct:-
- Every object moves with a constant speed.
- The time period the given pendulum is constant.
- 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.4– The 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.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 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,
Distance covered by the car = Final reading – Initial Reading
= 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.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.
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:
- A car moving with a constant speed.
- A car parked on a side road.
Ans.7– i.-
ii.-
Q.8– Which of the following regulations is correct?
- Speed = Distance * Time
- Speed = __Distance__
Time
iii. Speed = __Time__
Distance
- Speed = ______1_______
Distance * Time
Ans.8– ii. Speed = __Distance__
Time
Q.9– The basic unit of speed is:
- km/ h
- m/ min
iii. km/ h
- m/ s
Ans.9– iv. 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:-
- 100 km
- 25 km
iii. 15 km
- 10 km
Ans.10– ii. 25 km.
Q.11– Suppose 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.12– Fig 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.12– The Car ‘A’ is moving fast.
Q.13– Which of the following distance-time graphs shows a truck moving with speed which is not constant?
Ans.13– iii.