1. Classify the following as motion along a straight line, circular or oscillatory motion:

(i) Motion of your hands while running.

Ans: oscillatory motion.


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

Ans: straight line motion

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

Ans: circular motion

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

Ans: oscillatory motion

(v) Motion of the hammer of an electric bell.

Ans: oscillatory motion


(vi) Motion of a train on a straight bridge.

Ans: straight line motion



2. Which of the following are not correct?

(i) The basic unit of time is second.

Ans: This is correct.


(ii) Every object moves with a constant speed.

Ans: This is incorrect.


(iii) Distances between two cities are measured in kilometres.

Ans: This is correct.


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

Ans: This statement is generally incorrect.


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

Ans: This is correct.


3. A simple pendulum takes 32 s to complete 20 oscillations. What is the

time period of the pendulum?

Ans:  Time period of a pendulum is time taken by it to complete 1 oscillation. Hence, the time period of the pendulum is 1.6 seconds.


4. The distance between two stations is 240 km. A train takes 4 hours to

cover this distance. Calculate the speed of the train.

Ans: So the train takes 4 hours to travel a distance of 240 km between the two stations. So the train is supposed to travel with a constant velocity along a straight track. So the velocity of the train is 60 Km/hr.


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.

Ans: Distance covered by car = (57336 - 57321) km = 15 km Time taken between 08:30 AM to 08:50 AM = 20 minutes = 20/60 hour = 1/3 hour So Speed in km/min Speed = (Distance travelled)/ (Time) = (15km)/ (20min) = 0.75km/min Speed in km/h Speed = (Distance travelled)/ (Time) = (15km)/ (1/3h) = (15 x 3) km/ (1h) = 45km/h.


6. Salma 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.

Ans: If the bicycle has speed of 2m/s, calculate the distance between her house and the school. \ Converting into seconds, t= 15 x 60 = 900 seconds. Distance between her house and school = 1.8 km.


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.

Ans: 


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

Ans: (i) Speed = Distance / Time

9. The basic unit of speed is:

(i) km/min                      (ii) m/min

(iii) km/h                        (iv) m/s

Ans: (iv) m/s

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                    (v) 10 km

Ans:  (ii) 25 km.

11. Suppose the two photographs, shown in Fig. 9.1 and Fig. 9.2, 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.

Ans:


12. Fig. 9.15 shows the distance-time graph for the motion of two vehicles A and B. Which one of them is moving faster?








                                     Fig. 9.15 Distance-time graph for the motion of two cars

1. You 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 Fig. 9.16. One way to fix the gnomon could

be to make a groove along a diameter on the circular board.

Ans:

Next, 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 Fig. 9.16. 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 Fig. 9.16.

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 Fig. 9.16.


Ans:


2. Collect 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.

Ans:


Colour By: Himashree Bora.