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

Written by Team Trustudies
Updated at 2021-05-07

## NCERT solutions for class 7 Science Chapter 13 Motion And Time Exercise

Q.1 Classify the following as motion along a straight line, circular or oscillatory motion :
(i) Motion of your hands while running.
(ii) Motion of a horse pulling a cart on a straight road.
(iii) Motion of a child in a merry-go-round.
(iv) Motion of a child on a see-saw.
(v) Motion of the hammer of an electric bell.
(vi) Motion of a train on a straight bridge.

NCERT Solutions for Class 7 Science Chapter 13 Motion And Time

(i) Motion of your hands while running : Oscillatory motion.

(ii) Motion of a horse pulling a cart on a straight road : Motion along a straight line.

(iii) Motion of a child in a merry-go-round : Circular motion.

(iv) Motion of a child on a see-saw : Oscillatory motion.

(v) Motion of the hammer of an electric bell : Oscillatory motion.

(vi) Motion of a train on a straight bridge : Motion along a straight line

Q.2 Which of the following are not correct?
(i) The basic unit of time is second.
(ii) Every object moves with a constant speed.
(iii) Distances between two cities are measured in kilometres.
(iv) The time period of a given pendulum is constant.
(v) The speed of a train is expressed in m/h.

NCERT Solutions for Class 7 Science Chapter 13 Motion And Time

Incorrect statements are :

(ii) Every object moves with a constant speed.

(iv) The time period of a given pendulum is constant.

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

Q.3 A simple pendulum takes 32 s to complete 20 oscillations. What is the time period of the pendulum?

NCERT Solutions for Class 7 Science Chapter 13 Motion And Time

Number of oscillations = 20

Total time taken to complete 20 oscillations = 32 s

Time period = $$\frac{total time taken}{number of oscillation} = \frac {32}{20}$$ = 1.6 seconds

Therefore, the time period of the pendulum is 1.6 seconds.

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.

NCERT Solutions for Class 7 Science Chapter 13 Motion And Time

Distance = 240 km

Time taken = 4 hours

Speed =Distance covered/time taken = 240km/4 hours =60 km/h

Therefore , the speed of train is 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.

NCERT Solutions for Class 7 Science Chapter 13 Motion And Time

Initial reading of the odometer = 57321.0

Final reading of the odometer = 57336.0

Distance covered by the car = Final reading of the odometer - Initial reading of the odometer = 57336.0 km – 57321 km =15 km

Speed =$$\frac{15km}{20 min} =\frac{3}{4} km/min$$

Speed in km/hr =$$\frac{3}{4}$$ × 60 =(15 x 3) km/hr =45 km/hr.

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/min, calculate the distance between her house and the school.

NCERT Solutions for Class 7 Science Chapter 13 Motion And Time

Time taken by Salma to reach her school by bicycle = 15 mins= 15 x 60 = 900 s

Speed = 2 m/s

Distance = speed x time = 2 x 900= 1800 m

Also 1 km= 1000 m

Therefore 1800x (1/1000) = 1.8 km

Therefore, the distance between her house and the school is 1.8 km .

Q.7 Show the shape of the distance-time graph for the motion in the following cases :
(i) A car moving with a constant speed.
(ii) A car parked on a side road

NCERT Solutions for Class 7 Science Chapter 13 Motion And Time

Q.8 Which of the following relations is correct?
(i) Speed = Distance × Time
(ii) Speed = Distance/Time
(iii)Speed – Time/Distance
(iv)Speed = 1/Distance ×Time

NCERT Solutions for Class 7 Science Chapter 13 Motion And Time

(ii) Speed = Distance/Time

Q.9 The basic unit of speed is:
(i) km/min
(ii) m/min
(iii) km/h
(iv) m/s

NCERT Solutions for Class 7 Science Chapter 13 Motion And Time

(iii) km/h

Q.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

NCERT Solutions for Class 7 Science Chapter 13 Motion And Time

(ii) 25 km

Solution :

When the speed of the car is 40 km/h

Time taken = 15 min = 15/60 = 0.25 h

Speed formula : Distance covered d1 = speed x time taken = 40 x 0.25 = 10 kms

When the speed of the car is 60 km/ h

Speed formula : Distance covered d2 = speed x time taken = 60 x 0.25= 15 kms

Total distance covered by the car = d1 + d2 = 10 + 15 = 25 kms

Q.11 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.

NCERT Solutions for Class 7 Science Chapter 13 Motion And Time

The distance covered by the blue car 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 car = 120 m

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

Speed = distance/time = 120/10 = 12 m/sec

Q.12 Fig. 13.15 shows the distance-time graph for the motion of two vehicles A and B. Which one of them is moving faster?

NCERT Solutions for Class 7 Science Chapter 13 Motion And Time

Vehicle A is moving faster.

Solution: The graph is between distance and time .

Distance = speed x time

The slope for Vehcile A is more than that of Vehicle B.

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

NCERT Solutions for Class 7 Science Chapter 13 Motion And Time