Some lengths are given in Column I of Table 5.5. Some units are given in Column II. Match the lengths with the units suitable for measuring those lengths.
Table 5.5
| Column I | Column II |
|---|---|
| Distance between Delhi and Lucknow | centimetre |
| Thickness of a coin | kilometre |
| Length of an eraser | metre |
| Length of school ground | millimetre |
Answer
| Column I | Column II |
|---|---|
| Distance between Delhi and Lucknow | kilometre |
| Thickness of a coin | millimetre |
| Length of an eraser | centimetre |
| Length of school ground | metre |
Read the following statements and mark True (T) or False (F) against each.
(i) The motion of a car moving on a straight road is an example of linear motion.
(ii) Any object which is changing its position with respect to a reference point with time is said to be in motion.
(iii) 1 km = 100 cm
Answer
(i) True
(ii) True
(iii) False
Corrected Statement — 1 km = 1,00,000 cm (since 1 km = 1000 m and 1 m = 100 cm).
Which of the following is not a standard unit of measuring length?
- millimetre
- centimetre
- kilometre
- handspan
Answer
handspan
Reason — Millimetre, centimetre and kilometre are standard units of length, so the measurement of the same length made by different people does not differ. A handspan differs from person to person, so it is not a standard unit.
Search for the different scales or measuring tapes at your home and school. Find out the smallest value that can be measured using each of these scales. Record your observations in a tabular form.
Answer
The smallest value that can be measured using a scale is the length of its smallest division. A sample record of observations is given below.
| Measuring device | Smallest value that can be measured |
|---|---|
| 15-cm scale | 1 mm |
| Metre scale | 1 mm |
| Tailor's measuring tape | 1 mm |
| Long measuring tape (sports room) | 1 cm |
Suppose the distance between your school and home is 1.5 km. Express it in metres.
Answer
Given distance = 1.5 km
We know that 1 km = 1000 m.
∴ 1.5 km = 1.5 × 1000 m = 1500 m
Therefore, the distance between the school and home is 1500 m.
Take a tumbler or a bottle. Measure the length of the curved part of the base of glass or bottle and record it.
Answer
The base of a tumbler or bottle is curved, so it cannot be measured directly with a straight scale. Wrap a thread once around the curved part of the base, mark the point where it completes the round, and straighten the thread. Now measure the length of this thread using a metre scale. The reading gives the length of the curved part of the base.
For example, if the straightened thread measures 22 cm, then the length of the curved part of the base is 22 cm.
Measure the height of your friend and express it in (i) metres (ii) centimetres and (iii) millimetres.
Answer
Make your friend stand straight against a wall and mark the height with the help of an adult. Measure this height using a measuring tape.
Suppose the measured height of your friend is 1.4 m. Then,
(i) Height in metres = 1.4 m
(ii) Height in centimetres = 1.4 × 100 = 140 cm
(iii) Height in millimetres = 140 × 10 = 1400 mm
You are given a coin. Estimate how many coins are required to be placed one after the other lengthwise, without leaving any gap between them, to cover the whole length of the chosen side of a notebook. Verify your estimate by measuring the same side of the notebook and the size of the coin using a 15-cm scale.
Answer
First, estimate the number of coins by comparing the length of the chosen side of the notebook with the diameter of one coin. Then measure both lengths using a 15-cm scale and divide the length of the notebook's side by the diameter of the coin to check your estimate.
For example, if the notebook's side is 24 cm long and the coin is 2 cm across, then
Hence, 12 coins are required. If the division does not give a whole number, round up to the next whole coin to cover the entire length.
Give two examples each for linear, circular and oscillatory motion.
Answer
Linear motion:
Examples —
(i) a car moving on a straight road
(ii) an orange dropping from a tree.
Circular motion:
Examples —
(i) a stone tied to a thread and whirled in a circle
(ii) the motion of a merry-go-round.
Oscillatory motion:
Examples —
(i) the motion of a swing
(ii) the to and fro motion of an eraser hung from a thread.
Observe different objects around you. It is easier to express the lengths of some objects in mm, some in cm and some in m. Make a list of three objects in each category and enter them in the Table 5.6.
Table 5.6: Sizes of objects around us
| Size | Objects |
|---|---|
| mm | |
| cm | |
| m |
Answer
| Size | Objects |
|---|---|
| mm | Thickness of a coin, thickness of a page, length of a grain of rice |
| cm | Length of an eraser, length of a pencil, length of a comb |
| m | Height of a door, length of the classroom, height of a room |
A rollercoaster track is made in the shape shown in Fig. 5.19. A ball starts from point A and escapes through point F. Identify the types of motion of the ball on the rollercoaster and corresponding portions of the track.
Answer
The ball shows different types of motion on different portions of the track:
- From A to B: The track is a straight slope, so the ball moves along a straight line. This is linear motion.
- From B to C to D to E: The track forms a loop, so the ball moves along a circular path. This is circular motion.
- From E to F: The track is straight again, so the ball moves along a straight line. This is linear motion.
Tasneem wants to make a metre scale by herself. She considers the following materials for it—plywood, paper, cloth, stretchable rubber and steel. Which of these should she not use and why?
Answer
Tasneem should not use stretchable rubber, as its length changes when pulled and the distance between the scale markings would not remain fixed. Ordinary cloth may also stretch or shrink, while paper used on its own can fold, tear or lose its shape easily; these are not reliable choices for a durable metre scale.
Plywood and steel are more suitable because they are sufficiently rigid and maintain a fixed length.
Think, design and develop a card game on conversion of units of length to play with your friends.
Answer
A simple card game on conversion of units of length can be designed as follows:
- Prepare a set of cards. On each card, write a length in a particular unit, for example, 1 km, 1000 m, 100 cm, 1 m, 10 mm, 1 cm, and so on.
- Make pairs of cards that show equal lengths in different units, such as 1 km and 1000 m, or 1 m and 100 cm.
- Shuffle all the cards and place them face down on the table.
- Each player turns over two cards in turn. If the two cards show equal lengths (a correct conversion pair), the player keeps the pair and gets a point.
- If the cards do not match, they are turned face down again.
- The player who collects the most matching pairs wins the game.
This game helps players practise the conversions 1 km = 1000 m, 1 m = 100 cm and 1 cm = 10 mm in a fun way.