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NCERT Solutions for Class 7 Science Chapter 13
Motion and Time Class 7
Chapter 13 Motion and Time Exercise Solutions
<< Previous Chapter 12 : Reproduction in PlantsNext Chapter 14 : Electric Current and its Effects >>
Exercise : Solutions of Questions on Page Number : 156
Q1 :
Classify the following as motion along a straight line, circular oroscillatory 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.
Answer :
(i) Oscillatory motion
While running, the hands move to and fro and repeat their motion after a given interval of time. Hence, it is an oscillatory motion.
(ii)Straight line
The horse is pulling a cart on a straight road. Therefore, it has a motion along a straight line.
(iii)Circular motion
Merry-go-round has a circular motion. Therefore, a child sitting inside it will also have a circular motion.
(iv) Oscillatory motion
The child on a see-saw goes up and down continuously. It oscillates up-down. Therefore, it is an oscillatory motion.
(v)Oscillatory motion
The hammer hits the electric bell and vibrates rapidly. Therefore, it is an oscillatory motion.
(vi) Straight line
The train is moving on a straight bridge. Therefore, it has a motion along a straight line.
Q2 :
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 not constant.
(v) The speed of a train is expressed in m/h.
Answer :
(i) Correct
Second is the SI unit of time.
(ii) Not correct
An object can move with constant or variable speed.
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(iii) Correct
The distance between two cities can be very large. Since kilometre is a bigger unit of distance, the distance between two cities is
measured in kilometres. (iv) Not correct
Time period of a pendulum depends on the length of the thread. Hence, it is constant for a particular pendulum.
(v) Not correct
The speed of a train is measured either in km/h or in m/s.
Q3 :
A simple pendulum takes 32 s to complete 20 oscillations. What is the time period of the pendulum?
Answer :
Numberof oscillations = 20
Total time taken to complete 20 oscillations = 32 s
Q4 :
The distance between two stations is 240 km. A train takes 4 hours to cover this distance. Calculate the speed of the train.
Answer :
Distance between the two stations = 240 km
Time taken = 4 h
Q5 :
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.
Answer :
Initial reading of the odometer of the car = 57321.0 km
Final reading of the odometer of the car = 57336.0 km
Distance covered by the car
= Final reading of the odometer of the car - Initial reading of the odometer of the car
= 57336.0 - 57321.0 = 15 km
The given car starts at 8:30 a.m. and stops at 8:50 a.m.
Therefore, time taken by the car to cover the distance is (8:50 - 8:30) min = 20 min
Distance covered by the car = 15 km
Time taken by the car = 20 min
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NCERT Solutions for Class 7 Science Chapter 13
Motion and Time Class 7
Chapter 13 Motion and Time Exercise Solutions
<< Previous Chapter 12 : Reproduction in PlantsNext Chapter 14 : Electric Current and its Effects >>
Exercise : Solutions of Questions on Page Number : 156
Q1 :
Classify the following as motion along a straight line, circular oroscillatory 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.
Answer :
(i) Oscillatory motion
While running, the hands move to and fro and repeat their motion after a given interval of time. Hence, it is an oscillatory motion.
(ii)Straight line
The horse is pulling a cart on a straight road. Therefore, it has a motion along a straight line.
(iii)Circular motion
Merry-go-round has a circular motion. Therefore, a child sitting inside it will also have a circular motion.
(iv) Oscillatory motion
The child on a see-saw goes up and down continuously. It oscillates up-down. Therefore, it is an oscillatory motion.
(v)Oscillatory motion
The hammer hits the electric bell and vibrates rapidly. Therefore, it is an oscillatory motion.
(vi) Straight line
The train is moving on a straight bridge. Therefore, it has a motion along a straight line.
Q2 :
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 not constant.
(v) The speed of a train is expressed in m/h.
Answer :
(i) Correct
Second is the SI unit of time.
(ii) Not correct
An object can move with constant or variable speed.
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(iii) Correct
The distance between two cities can be very large. Since kilometre is a bigger unit of distance, the distance between two cities is
measured in kilometres. (iv) Not correct
Time period of a pendulum depends on the length of the thread. Hence, it is constant for a particular pendulum.
(v) Not correct
The speed of a train is measured either in km/h or in m/s.
Q3 :
A simple pendulum takes 32 s to complete 20 oscillations. What is the time period of the pendulum?
Answer :
Numberof oscillations = 20
Total time taken to complete 20 oscillations = 32 s
Q4 :
The distance between two stations is 240 km. A train takes 4 hours to cover this distance. Calculate the speed of the train.
Answer :
Distance between the two stations = 240 km
Time taken = 4 h
Q5 :
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.
Answer :
Initial reading of the odometer of the car = 57321.0 km
Final reading of the odometer of the car = 57336.0 km
Distance covered by the car
= Final reading of the odometer of the car - Initial reading of the odometer of the car
= 57336.0 - 57321.0 = 15 km
The given car starts at 8:30 a.m. and stops at 8:50 a.m.
Therefore, time taken by the car to cover the distance is (8:50 - 8:30) min = 20 min
Distance covered by the car = 15 km
Time taken by the car = 20 min
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