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Motion and Time Class 7, , Chapter 13 Motion and Time Exercise Solutions, , Exercise : Solutions of Questions on Page Number ; 156, , Qi:, Classify the following as motion along a straight line, circular oroscillatory motion:, , (I) Motion of your hands whlle running., , (li) Motion of a horse pulling a cart on a stralght road., (il) Motion of a child In a merry-go-round., , (Iv) Motion of a child ona see-saw., , (v) Motion of the hammer of an electric bell., , {vi) Motion of a train ona 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,, , , , aed of the following are not correct?, , (Il) The basic unit of time Is second., , (li) Every object moves with a constant speed., (lil) Distances between two cities are measured in kllometres., , (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 St unit of time., , (ii) Not correct, An object can move with constant or variable speed., , , , Scanned with CamScanner

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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: “ sa A naa ea, A simple pendulum takes 32 s to complete 20 oscillations. What Is the timo period of the pendulum?, , , , Answer:, Numberof oscillations = 20, , Total time taken to complete 20 oscillations = 32 s, , Time period ___Total time taken _ 32 165, , Number of oscillations 20, , , , , , Qa:, 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 = 4h, Distance. _ 240 45, Speed == 0 keh, Peer Time taken 4 :, , , , Qs:, 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 kmi/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, , = §7336.0 - 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, , Di i" povered che, , Se, , , , , , , Scanned with CamScanner

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Again,, , 60 min= 1h, 1 1, , 20 min = —x20=—h, 60 3, , th, , Time taken by the car= 3, , . Distance covered _15 = 45 kwh, , , , Speed, Time taken I, 3 ; _ een —, a6: a speed of 2 m/s, calculate the, Salma takes 18 minutes from her house to reach her achool on a bleycle. if the bleycle has 2 SP9, , , , distance between her house and the school., , Answer:, Time taken by Salma to reach her school from her home = 15 min = 15 x 60 = 900s, , Speed of her bicycle = 2 m/s, , Distance covered, Time taken, Distance covered = Speed *Time taken = 2 x900 = 1800 m 1000, , Speed =, , m=tkm, , £1800 m=—1-x1800=18 km, , , , a7:, Show the shape of the distance-time graph for the motion In the following cases:, (I) Acar moving with a constant speed., , (Il) A car parked on a side road., , Answer:, , (i) Acar moving with a constant speed covers equal distance in equal intervals of time. Such motion of car is re sented In the, given distance-time graph. a, , Scanned with CamScanner

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(iiyThe 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. :, , 4, , , , , , QB:, Which of the following relations Is correct?, , (i) Speed = Distance * Time, , Speed Distance., wo Time, Speed = = inne, , , , ID}, , Answer:, (ii) Speed of an object is given by the relation, , , , Time, , , , , Qe:, The basic unit of speed Is:, , (i) km/min, (li) mimin, (iil) km/h, {iv) mis, Answer :, , (iv)m/s, The basic unit of distance is metre (m)., , The basic unit of time is second (8)., Speed = Distance = ad, Time, Therefore, the basic unit of speed is m/s., , , , , , , Scanned with CamScanner

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Q10;, , Acar mo:, ves with a speed of 40 kmih for 15 minutes and then with a speed of 60 km/h for, , distance covered by the car Is:, , () 100 km, (UW) 28 km, (i) 15 km, (lv) 10 km, Answer :, (ii)25 km, Case |, Speed of the car = 40 km/h, 15, Time taken = 15 min= wo °5 b, Distance covered, , , , Speed =, Time taken, Distance covered, d= Speed xTime taken = 40 «0.25 = 10 km, , Case Il, Speed of the car = 60 km/h, , 13 92s, , Time taken = 15 min =, , Distance covered, , Speed = ———___——, Time taken, , Distance covered. o:= Speed «Time taken = 60 «0.25 = 15 km, , overed by the car,, , Total distance c, .d by the car is 25 km., , the total distance covere', , , , Qit:, Suppose the two photographs,, 4100 metres Is shown by 1 cm In these photo, , d= dt d= 10 +15 = 25 km Therefore,, , shown In Figure 1 and Figure 2, had been taken a!, graphs, calculate the speed of the blue car., , the next 15 minutes. The totaj, , , , t an Interval of 10 seconds. If a distance of, , Scanned with CamScanner