TEXTBOOK QUESTIONS AND THEIR ANSWERS. Q.1. Table below gives some common examples of motions. Identify the types of motion in each case.

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1 13 MOTION AND TIME TEXTBOOK QUESTIONS AND THEIR ANSWERS Q.1. Table below gives some common examples of motions. Identify the types of motion in each case. Table : Some examples of different types of motion Example of motion Type of motion Along a straight line/circular/periodic Soldiers in a march past Bullock cart moving on a straight road Hands of an athlete in a race Pedal of a bicycle in motion Motion of the earth around the sun Motion of a swing Motion of a pendulum 1

2 Ans. Example of motion Type of motion Along a straight line / circular/periodic Soldiers in a march past Bullock cart moving on a straight road Hands of an athlete in a race Pedal of a bicycle in motion Motion of the earth around the sun Motion of a swing Motion of a pendulum Along a straight line Along a straight line Periodic Circular Periodic Periodic Periodic Q.2. Paheli wondered how time was measured when pendulum clocks were not available. Ans. Time was measured by following the position of the sun, by sand clock, water clock etc, when pendulum clocks were not available. 2

3 Q.3. Boojho wants to know whether there is any device that measures the speed. Ans. Speed can be measured by a device called speedometer. Q.4.Calculate the following speeds in m/s. Table : Fastest speed that some animals can attain S.No. Name of the Speed in Speed in m/s object km/h 1. Falcon / 0/ 60/ 60/ 2. Cheetah Blue Fish Rabbit Squirrel Domestic mouse Human Giant Tortoise Snail

4 Ans. 4

5 S.No. Name of the object Speed in km/h Speed in m/s 1. Falcon m/s 9 2. Cheetah m/s 9 3. Blue Fish m/s Rabbit Squirrel m/s m/s Domestic mouse m/s Human Giant Tortoise m/s 9 27 m/s Snail m/s 72 Q.5. Classify the following as motion along a straight line, circular or oscillatory motion : 5

6 (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. Ans. (i) Oscillatory motion. (ii) Motion along a straight line. (iii) Circular motion. (iv) Oscillatory motion. (v) Motion along a straight line. (vi) Motion along a straight line. Q.6. Which of the following are not correct? (i) The basic unit of time is second. Ans. True. 6

7 (ii) Every object moves with a constant speed. Ans. False. (iii) Distances between two cities are measured in kilometres. Ans. True. (iv) The time period of a given pendulum is not constant. Ans. False. (v) The speed of a train is expressed in m/h. Ans. False. Q.7. A simple pendulum takes 32 s to complete 20 oscillations. What is the time period of the pendulum? Ans. Given, pendulum takes 32 s to complete 20 oscillations Time period =? Time period = 32 =1.6s 20 7

8 Q.8. The distance between two stations is 240 km. A train takes 4 hours to cover this distance. Calculate the speed of the train. Ans. Given, distance between two stations = 240 km. Time taken to cover the distance = 4 hours. Now, Speed =? Distance 240 Speed = Time-taken 4 = 60 km/h Q.9. The odometer of a car reads 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 km? Calculate the speed of the car in km/min during this time. Express the speed in km/h also. Ans. Initial odometer reading = km Final odometer reading = km Total distance covered = Final odometer reading initial odometer reading = km km 8

9 = 15.0 km Initial time = 8.30 am Final time = 8.50 am Total time taken = Final time Initial time = 8.50 am 8.30 am Speed= = 20 min. Total distance covered Total time-taken = 15.0 km = 0.75 km / min 20 min Speed in km/h = = 45 km / h (1 h = 60 min). Q.10. Salma takes 15 minutes form her house to reach school on a bicycle. If the bicycle has a speed of 2 m/s, calculate the distance between her house and the school. Ans.Time taken by Salma to reach her school = 15 min. 9

10 = = 900 s Speed = 2 m/s Distance = Speed Time = 2 m/s 900 s Distance = 1800 m. Q.11. 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. Ans. Distance Distance O (i) Time O (ii) Time 10

11 Q.12. Which of the following relations is correct? (i) Speed = Distance Time (ii) Speed = Distance Time (iii) Speed = Distance Time (iv) 1 Speed = Distance Time Ans. (ii) Speed Distance Time Q.13. The basic unit of speed is : (i) km / min. (iii) km / h (ii) m / min. (iv) m/s. Ans. (iv) m/s Q.14. 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 Ans. (ii) 25 km 11

12 Q.15. Suppose the two photographs shown in Fig. I and Fig. II below, had been taken at an interval of 10 seconds. If a distance of 100 metres is shown by 1 cm in the photographs. Calculate the speed of the blue car. Ans. S = Distance peed = Time 100 = 10 m/s 10 s Q.16. Fig. below shows the distance time graph for the motion of two vehicles A and B. Which one of them is moving faster? A B Distance Time Fig : Distance-time graph for the motion of two cars Ans. Car A is moving faster. 12

13 Q.17. Which of the following distance time graphs shows a truck moving with speed which is not constant? (i) (ii) Distance Distance (iii) Time (iv) Time Distance Distance Time Time Ans. (iii) 13