{"id":24425,"date":"2021-06-17T12:02:19","date_gmt":"2021-06-17T06:32:19","guid":{"rendered":"https:\/\/mcq-questions.com\/?p=24425"},"modified":"2022-03-02T10:38:19","modified_gmt":"2022-03-02T05:08:19","slug":"ncert-solutions-for-class-7-science-chapter-13","status":"publish","type":"post","link":"https:\/\/mcq-questions.com\/ncert-solutions-for-class-7-science-chapter-13\/","title":{"rendered":"NCERT Solutions for Class 7 Science Chapter 13 Motion and Time"},"content":{"rendered":"

These NCERT Solutions for Class 7 Science<\/a> Chapter 13 Motion and Time Questions and Answers are prepared by our highly skilled subject experts to help students while preparing for their exams.<\/p>\n

Motion and Time NCERT Solutions for Class 7 Science Chapter 13<\/h2>\n

Class 7 Science Chapter 13 Motion and Time Textbook Exercise Questions and Answers<\/h3>\n

Question 1.
\nClassify the following as motion along a straight line, circular or oscillatory motion:
\na. Motion of your hands while running.
\nb. Motion of a horse pulling a cart on a straight road.
\nc. Motion of a child in a merry-go-round.
\nd. Motion of a child on a see-saw.
\ne. Motion of the hammer of an electric bell.
\nf. Motion of a train on a straight bridge.
\nAnswer:
\na. Oscillatory motion
\nb. Along a straight line (rectilinear motion)
\nc. Circular motion
\nd. Oscillatory motion
\ne. Oscillatory motion
\nf. Rectilinear motion<\/p>\n

Question 2.
\nWhich of the following are not correct?
\na. The basic unit of time is second.
\nb. Every object moves with a constant speed.
\nc. Distances between two cities are measured in kilometres.
\nd. The time period of a given pendulum is not constant.
\ne. The speed of a train is expressed in m\/h.
\nAnswer:
\nb., d. and e.<\/p>\n

Question 3.
\nA simple pendulum takes 32 s to complete 20 oscillations. What is the time period of the pendulum?
\nAnswer:
\nNumber of oscillations = 20
\nTotal time taken to complete 20 oscillations = 32 s
\nTime period = \\(\\frac{\\text { Total time taken }}{\\text { Number of oscillations }}\\)
\n= \\(\\frac {32}{20}\\) = 1.6 s<\/p>\n

Question 4.
\nThe distance between two stations is 240 km. A train takes 4 hours to cover this distance. Calculate the speed of the train.
\nAnswer:
\nDistance between two stations = 240 km
\nTime taken = 4 h
\nSpeed = \\(\\frac{\\text { Distance }}{\\text { Time taken }}\\) = \\(\\frac {240}{4}\\) = 60 km\/h<\/p>\n

\"NCERT<\/p>\n

Question 5.
\nThe 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.
\nAnswer:
\nInitial reading of the odometer of the car = 57321.0 km
\nFinal reading of the odometer of the car = 57336.0 km
\nDistance covered by the car = Final reading of the odometer – Initial reading of the odometer
\n= 57336.0 – 57321.0 km = 15 km
\nThe given car starts at 8:30 AM and stops at 8:50 AM.
\nTherefore, time taken by the car to cover the distance is (8:50 – 8:30) min = 20 min
\nDistance covered by the car = 15 km
\nTime taken by the car = 20 min
\nSpeed = \\(\\frac{\\text { Distance covered }}{\\text { Time taken }}\\)
\n= \\(\\frac{15 \\mathrm{~km}}{20 \\mathrm{~min}}\\)
\n= 0.75 km\/min
\nAgain,
\n60 min = 1 h
\n20 min = \\(\\frac {1}{60}\\) \u00d7 20 = \\(\\frac {1}{3}\\)h
\nTime taken by the car = \\(\\frac {1}{3}\\)h
\nSpeed = \\(\\frac{\\text { Distance covered }}{\\text { Time taken }}\\)
\n= \\(\\frac{15 \\mathrm{~km}}{\\left(\\frac{1}{3}\\right) \\mathrm{h}}\\)
\n= 45 km\/h<\/p>\n

Question 6.
\nSalma 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.
\nAnswer:
\nTime taken by Salma to reach her school from her home = 15 min
\n= 15 \u00d7 60 = 900 s
\nSpeed of her bicycle = 2 m\/s
\nDistance covered = Speed \u00d7 Time taken = 2 \u00d7 900= 1800 m
\n1000 m = 1 km
\n\u2234 Distance = \\(\\frac {1}{1000}\\) \u00d7 1800 = 1.8 km<\/p>\n

Question 7.
\nShow the shape of the distance-time graph for the motion in the following cases:
\na. A car moving with a constant speed.
\nb. A car parked on a side road.
\nAnswer:
\na. A car moving with a constant speed covers equal distances in equal intervals of time. Such motion of car is represented by the given distance-time graph.
\n\"NCERT
\nb. The distance-time graph of a car parked on a road side is such that with the increase in time, there is no change in distance, as shown in the given figure.
\n\"NCERT<\/p>\n

Question 8.
\nWhich of the following relations is correct?
\na. Speed = Distance \u00d7 Time
\nb. Speed = Distance\/Time
\nc. Speed = Time\/Distance
\nd. Speed = 1\/Distance Time
\nAnswer:
\nb. Speed = Distance \u00d7 Time<\/p>\n

Question 9.
\nThe basic unit of speed is
\na. km\/min
\nb. m\/min
\nc. km\/h
\nd. m\/s
\nAnswer:
\nd. m\/s<\/p>\n

\"NCERT<\/p>\n

Question 10.
\nA 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:
\na. 100 km
\nb. 25 km
\nc. 15 km
\nd. 10 km
\nAnswer:
\nb. 25 km
\nFirst, the car is moving with 40km\/h for 15 minutes.
\n15 minutes = 15\/60 h = 1\/4 h
\nDistance covered = 40 \u00d7 1\/4 = 10 km
\nSecond, the car is moving with 60 km\/h for 15 minutes.
\nDistance covered = 60 \u00d7 1\/4 = 15 km
\nTotal distance covered = 10 km + 15 km = 25 km<\/p>\n

Question 11.
\nSuppose the two photographs, shown below, had been taken at an interval of 10 seconds. If a distance of 100 meters is shown by 1 cm in these photographs, calculate the speed of the blue car (circled).
\n\"NCERT
\n\"NCERT
\nAnswer:
\nFirst, measure the distance moved by the car with the help of scale and then proceed as given below.
\nSuppose the distance measured by the scale is 2 cm.
\nMultiply 2 with 100 to get the actual distance = 2 \u00d7 100 = 200 m.
\n(given, 1cm = 100 m)
\nInterval of time between the photos taken = 10 s.
\nSpeed of the blue car = 200\/10 = 20 m\/s<\/p>\n

Question 12.
\nFigure given here shows the distance-time graph for the motion of two vehicles A and B. Which one of them is moving faster?
\n\"NCERT
\nDistance-time graph for the motion of two cars
\nAnswer:
\nVehicle A is moving faster which is evident from the higher slope for distance-time graph of this vehicle compared to that of the other vehicle.<\/p>\n

Question 13.
\nWhich of the following distance-time graphs shows a truck moving with speed which is not constant?
\n\"NCERT
\nAnswer:
\n(c) The slope of the graph in this option is not a straight line and hence it does not show a uniform motion.<\/p>\n

NCERT Extended Learning Activities and Projects<\/span><\/p>\n

Question 1.
\nYou can make your own sundial and use it to mark the time of the day at your place. First of all find the latitude of your city with the help of an atlas. Cut out a triangular piece of a cardboard such that its one angle is equal to the latitude of your place and the angle opposite to it is a right angle. Fix this piece, called gnomon, vertically along a diameter of a circular board a shown in the figure. One way to fix the gnomon could be to make a groove along a diameter on the circular board.
\n\"NCERT
\nNext, select an open space, which receives sunlight for most of the day. Mark a line on the ground along the North-South direction. Place the sundial in the sun as shown in the figure. Mark the position of the tip of the shadow of the gnomon on the circular board as early in the day as possible, say 8:00 AM. Mark the position of the tip of the shadow every hour throughout the day. Draw lines to connect each point marked by you with the centre of the base of the gnomon as shown in the figure. Extend the lines on the circular board up to its periphery. You can use this sundial to read the time of the day at your place. Remember that the gnomon should always be placed in the North-South direction as shown in the figure.
\nHint:
\nDo it yourself.<\/p>\n

\"NCERT<\/p>\n

Question 2.
\nCollect information about time-measuring devices that were used in the ancient times in different parts of the world. Prepare a brief write up on each one of them. The write up may include the name of the device, the place of its origin, the period when it was used, the unit in which the time was measured by it and a drawing or a photograph of the device, if available.
\nHint:
\na. Sundials and Obelisks: In 1500 B.C. simple sundials were used to divide the time interval between sunrise and sunset in 12 different parts. The Ancient Egyptian Obelisk, constructed about 3500 B.C. was the oldest shadow clock used to measure time. The shadows that move to different marks enabled the Egyptians to calculate time which helped to divide the day into two parts.<\/p>\n

b. Sand-glass: It is also called an hourglass, made up of two conical glasses connected vertically by the narrow neck, came into being in the 14th Century. It could measure passage of specific time period depending upon the size and width of the glass and the quantity of sand in it.<\/p>\n

c. Water clock: It was known to have existed in Babylon in Egypt around 16th Century. It was used to measure time observing steady flow of water from or into a container. Measurements were marked on the container but there were variations due to the pressure of water flow.<\/p>\n

d. Candle clock: The candle was marked with numbers and the burning of wax indicated a specific period of time. It is unknown where the candle clocks were used although it was first referred by a Chinese poet called You Jiangu in 520 A.D.<\/p>\n

e. Pendulum: A scientific study was done around 1602 by an Italian astronomer Galileo Galilei on pendulum where its motion was used to keep a track of time. It was considered to be the the world\u2019s most accurate time-keeping invention until 1930. The pendulum clock was invented by Christian Huygens in the year 1658 which was used till 270 years.<\/p>\n

f. The Quartz: In early 20th Century, Albert Einstein proposed theories of relativity and defined time as the fourth dimension. The quartz clocks were developed in 1930 which were far more improvised version of a pendulum clock. The quartz crystal has to be placed in the suitable circuit in a way that creates vibrations in the crystal to generate a constant frequency. This is used to operate electronic clock display.<\/p>\n

g. Last, the atomic and laser invention in 1960\u2019s has changed the measurement of time forever. These are the most accurate clocks so far.<\/p>\n

Question 3.
\nMake a model of a sand clock which can measure a time interval of 2 minutes.
\n\"NCERT
\nHint:
\nDo it yourself.<\/p>\n

Question 4.
\nYou can perform an interesting activity when you visit a park to ride a swing. You will require a watch. Make the swing oscillate without anyone sitting on it. Find its time period in the same way as you did for the pendulum. Make sure that there are no jerks in the motion of the swing. Ask one of your friends to sit on the swing. Push it once and let it swing naturally. Again measure its time period. Repeat the activity with different persons sitting on the swing. Compare the time period of the swing measured in different cases. What conclusions do you draw from this activity?
\nHint:
\nWe can conclude that the time period of a pendulum depends on the acceleration due to gravity and the length of the suspension. So keeping those constant, the time period of the simple pendulum will remain constant. It will not change with changing mass or weight of bob (people sifting on the swing).<\/p>\n

Activity 1<\/span><\/p>\n

Objective: To show that some objects moves fast and some objects move slow.
\nMaterial Required: Pen and paper.
\nProcedure:<\/p>\n