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#### Page No 147:

#### Question 1:

Which is the correct order of units form largest to smallest?

(a) millimetre, centimetre, kilometre

(b) centimetre, millimetre, kilometre

(c) kilometre, millimetre, centimetre

(d) kilometre, centimetre, millimetre

#### Answer:

(d) kilometre, centimetre, millimetre

1 kilometre = 1000 metre

1 metre = 100 centimetre

1 centimetre = 10 millimetre

Hence, kilometre is the largest unit and millimetre is the smallest.

#### Page No 147:

#### Question 2:

The reason scientists repeat measurements they take during experiments is so that they can

(a) check whether the instruments used are inaccurate.

(b) list the measurements taken in a table.

(c) take the average and reduce the possibility of an error.

(d) get more than one answer.

#### Answer:

(c) take the average and reduce the possibility of an error.

Repeated measurements reduce the possibility of error and using an average of all the measurements is the best way to reduce error.

#### Page No 148:

#### Question 3:

The captain of a football team is measuring the heights of his team members. The measurement for one player is written as 1.9. What unit of measure is most probably being used?

(a) km

(b) m

(c) cm

(d) mm

#### Answer:

(b) m

A human can not be as short as 1.9 cm or mm, neither he could be as tall as 1.9 km. The captain must be measuring heights of his team members in metres.

#### Page No 148:

#### Question 4:

The average length of the three paper clips shown is

(a) 2.0 cm

(b) 2.2 cm

(c) 2.5 cm

(d) 3.0 cm

Figure

#### Answer:

(b) 2.2 cm

$\mathrm{Average}\mathrm{length}=\frac{2.2+2+2.4}{3}\phantom{\rule{0ex}{0ex}}=2.2\mathrm{cm}$

#### Page No 148:

#### Question 5:

The distance between two towns is 3 km 260 m. This is same as

(a) 30260 m

(b) 3260 m

(c) 3620 m

(d) 300260 m

#### Answer:

(b) 3260 m

$\because $ 1 km = 1000 metre

$\therefore $ 3 km 260 m = 3000 m + 260 m

= 3260 m

#### Page No 148:

#### Question 6:

Which of the following shows the correct position of the eye while taking a reading of the scale?

(a) C

(b) B

(c) A

(d) all of these

Figure

#### Answer:

(b) B

While taking the reading of the scale, our eyes must be exactly above and in line with the reading.

#### Page No 148:

#### Question 7:

A teacher asked her students to measure the length of their classroom.

Rekha said, 'I can do it by counting my footsteps.'

Renu said, 'I will measure it using my skipping rope.'

Ramesh said, 'I will measure it using a measuring tape.'

Which of these is true?

(a) Only Rekha will be able to measure the room's length.

(b) Only Ramesh will be able to do that.

(c) All will be able to do it, but Renu's method is best.

(d) All will be able to do it, but Ramesh' method is best.

#### Answer:

(d) All will be able to do it, but Ramesh’s method is best.

Measuring tape is the best instrument to measure length accurately among the given options. Hence, Ramesh’s method is the best.

#### Page No 148:

#### Question 8:

Which is the correct method to express 35 cm in metres?

(a) 35 × 100 m

(b) 35 × 1000 m

(c) 35 ÷ 100 m

(d) 35 ÷ 1000 m

#### Answer:

(a) 35 ÷ 100 m

$\because $ 100 cm = 1 m

$\therefore $ 35 cm = 35 ÷ 100 m

#### Page No 148:

#### Question 9:

The thickness of a book containing 100 pages is 2 cm 5 mm. The thickness of one page will be

(a) 0.25 mm.

(b) 0.25 cm.

(c) 25 mm.

(d) 2.5 mm.

#### Answer:

(a) 0.25 mm

$\because $ 1 cm = 10 mm

$\therefore $ 2 cm 5 mm = 2 × 10 mm + 5 mm

= 25 mm

Now, thickness of 100 pages = 25 mm

$\therefore $ Thickness of 1 page = 25 ÷ 100 mm

= 0.25 mm

#### Page No 148:

#### Question 10:

One oscillation of a pendulum is

(a) the time taken for a complete to and fro movement.

(b) the distance travelled by the bob from the mean position.

(c) the movement of the bob from one extreme position to the other extreme.

(d) one complete to and fro movement about the mean position.

#### Answer:

(d) one complete to and fro movement about the mean position.

One oscillation of a pendulum is one cycle in its motion. The cycle includes the movement of pendulum from mean position to one extreme position then to the mean position and then to the other extreme position and return to the mean position.

#### Page No 148:

#### Question 11:

The time period of a pendulum is

(a) the time taken for the bob to move from one extreme position to the other.

(b) the time taken by the bob for one complete to and fro motion about the mean position.

(c) the time taken by the bob to go from the rest position to one extreme and return to the rest position.

(d) none of the above.

#### Answer:

(a) the time taken by the bob for one complete to and fro motion about the mean position.

Time period of a pendulum is the time taken by the pendulum to complete one oscillation.

#### Page No 149:

#### Question 12:

The amplitude of a pendulum is

(a) the time taken for one complete oscillation.

(b) the time taken for half an oscillation.

(c) the distance between the mean position and one extreme position.

(d) the distance between one extreme position and the other extreme position.

#### Answer:

(a) the distance between the mean position and one extreme position

The amplitude of a pendulum is the distance travelled by the pendulum from the mean position to the extreme position.

#### Page No 149:

#### Question 13:

What is common to the following?

the propeller of a flying helicopter; the second hand of a watch; the tape of a cassette recorder

(a) examples of translatory motion

(b) examples of oscillatory motion

(c) examples of rotatory motion

(d) examples of periodic motion

#### Answer:

(a) examples of rotatory motion

When every point on a moving body moves around a fixed centre or an axis of rotation, the motion is called rotatory motion. The propeller of a flying helicopter, the second hand of a watch and the tape of a cassette recorder moves around a fixed centre. Hence, these are examples of rotatory motion.

#### Page No 149:

#### Question 14:

A dozen identical coins were stacked one above the other. Their total height was 3 cm 6 mm.

What is the thickness of one coin?

#### Answer:

One dozen coins = 12 coins

Total height of 12 coins = 3 cm 6 mm

= 3 × 10 mm + 6 mm

= 36 mm

Therefore, thickness of one coin = 36 ÷ 12

= 3 mm

#### Page No 149:

#### Question 15:

Ten similar coins were stacked one above the other. When measured with a scale, the readings at the top and bottom were 1.5 cm and 4.0 cm respectively. What is the thickness of each coin?

#### Answer:

Total thickness of 10 coins = 4.0 cm – 1.5 cm

= 2.5 cm

Therefore, thickness of each coin = 2.5 cm ÷ 10

= 0.25 cm

#### Page No 149:

#### Question 16:

A dozen shirt buttons of the same size were arranged one above the other. Their total height was 2 cm 4 mm. What is the thickness of one button?

#### Answer:

A dozen buttons = 12 buttons

Total thickness of 12 buttons = 2 cm 4 mm

= 2 × 10 mm + 4 mm

= 24 mm

Therefore. thickness of one button = 24 mm ÷ 12

= 2 mm

#### Page No 149:

#### Question 17:

Why do we need standard units of measurement?

#### Answer:

We need standard units of measurement to have a common set of units that can be used everywhere.

#### Page No 149:

#### Question 18:

Complete the following.

(a) 8754 cm = _________ m ________ cm

(b) 9278 m =___________ km ________ m

(c) 52 mm =___________ cm _________ mm

(d) 96 km 33 m = _______ m

(e) 50 m 23 cm = _______ cm

(f) 1 cm 9 mm = ________ mm

#### Answer:

(a) 8754 cm = __87__ m __54__ cm

(b) 9278 km = __9__ km __278__ m

(c) 52 mm = __5__ cm __2__ mm

(d) 96 km 33 m = __96033__ m

(e) 50 m 23 cm = __5023__ cm

(f) 1 cm 9 mm = __19__ mm

#### Page No 149:

#### Question 19:

What unit of length will be used to express:

(a) the distance between Mumbai and Pune?

(b) the length of your jeans?

(c) the length of a medicine capsule?

(d) the circumference of your wrist?

#### Answer:

(a) The distance between Mumbai and Pune will be measured in kilometre.

(b) The length of jeans will be measured in inches.

(c) The length of a medicine capsule will be measured in millimetre.

(d) The circumference of wrist will be measured in inches.

#### Page No 149:

#### Question 20:

Mark the following statements as true or false.

(a) The standard unit for measuring length is 1 metre.

(b) There are one thousand centimetres in a metre.

(c) The length of an earthworm can be best measured in cm or mm.

(d) The length of a room is 4 m 65 cm. This is the same as 4065 cm.

(e) A passenger in a flying aeroplane is at rest with respect to the airport and moving with respect to other passengers.

(f) All of us on the earth are always at rest with respect to each other but moving with respect to the sun and the other bodies in the universe.

#### Answer:

(a) True

(b) False

There are one hundred centimetres in one metre.

(c) True

(d) False

The length of a room is 4 m 65 cm.

4 m 65 cm = 4 × 100 cm + 65 cm = 465 cm

(e) False

A passenger in a flying aeroplane is moving with respect to the airport and is at rest with respect to other passengers.

(f) True

#### Page No 149:

#### Question 21:

An object can show different types of motion at the same time. In a sewing machine used by tailors, mention the type of motion each of the following have:

(a) the wheel

(b) the needle

(c) the cloth

#### Answer:

(a) The wheel has rotatory motion.

(b) The needle has oscillatory motion.

(c) The cloth has translatory motion.

#### Page No 150:

#### Question 22:

Write down whether the following motions are: translatory rectilinear (R), translatory curvilinear (C), rotatory (RO) or oscillatory (O).

(a) the movement of a roller coaster

(b) the movement of the hand while writing the letter 'O'

(c) the motion of the blades of a mixer

(d) the motion of a child sliding down a slide

(e) the movement of the wings of a bird

(f) the movement of a baby's cradle

(g) the movement of the hour hand of a clock

(h) the movement of a rocking chair

(i) the movement of a bucket as it draws water from a well

(j) the movement of the pulley while drawing water from a well

#### Answer:

(a) translatory curvilinear (C)

(b) translatory curvilinear (C)

(c) Rotatory (RO)

(d) Translatory rectilinear (R)

(e) Oscillatory (O)

(f) Oscillatory (O)

(g) Rotatory (RO)

(h) Oscillatory (O)

(i) Translatory rectilinear (R)

(j) Rotatory (RO)

#### Page No 150:

#### Question 23:

The chart below shows the amount of rainfall recorded in Delhi for a week in July. Study the graph and answer the questions the follow.

Figure

(a) On which days was the rainfall the same?

(b) What happened on Wednesday?

(c) Calculate the average rainfall for this week.

#### Answer:

(a) Rainfalls were same on Sunday and Tuesday and on Friday and Saturday.

(b) There was no rainfall on Wednesday.

(c) Average rainfall $=\frac{17+20+\hspace{0.17em}17+\hspace{0.17em}5+\hspace{0.17em}15+\hspace{0.17em}15}{7}$

= 12.7 mm

#### Page No 150:

#### Question 24:

(a) Draw a neat, labelled diagram of an oscillating pendulum and label the following: mean position, extreme position, amplitude.

(b) Explain one oscillation with the help of the diagram.

(c) Define the following terms: one oscillation, time period of an oscillation, amplitude

#### Answer:

(a)

(b)

One oscillation is the distance travelled by the pendulum from mean position to one extreme position, coming back to mean position, going to the other extreme position and then again coming back to mean position.

(c)

One oscillation is the distance travelled by the pendulum from mean position to one extreme position, coming back to mean position, going to the other extreme position and then again coming back to mean position.

Time period is the time taken by the pendulum to complete one oscillation.

Amplitude of a pendulum is the distance from mean position to any of the extreme positions.

#### Page No 150:

#### Question 25:

What is periodic motion? Explain with an example.

#### Answer:

Periodic motion is a type of motion that repeats itself. For example, motion of earth around the sun is periodic because earth completes a full revolution in one year and continues to revolve.

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