Science Chapter 5: Measurement of Length and Motion - Exercises

📘 Chapter 5: Measurement of Length and Motion

📝 “Let us enhance our learning” (Exercises)

Question 1. 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.

Answer (Correct Matching):

Column I (Length) Column II (Suitable Unit)
Distance between Delhi and Lucknow kilometre
Thickness of a coin millimetre
Length of an eraser centimetre
Length of school ground metre

Question 2. Read the following statements and mark True (T) or False (F) against each:

No. Statement True / False
(i) The motion of a car moving on a straight road is an example of linear motion. [ T ]
(ii) Any object which is changing its position with respect to a reference point with time is said to be in motion. [ T ]
(iii) 1 km = 100 cm [ F ]

Explanation: (iii) False: 1 km = 1000 m and 1 m = 100 cm, therefore 1 km = 1,00,000 cm.

Question 3. Which of the following is not a standard unit of measuring length?
(i) millimetre (ii) centimetre (iii) kilometre (iv) handspan

  • Answer: (iv) handspan
  • Reason: Handspan varies from person to person, so it is not a standardized or universal unit of measurement.

Question 4. 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.

Measuring Scale / Device Smallest Value (Least Count)
15-cm geometry box scale 1 mm (or 0.1 cm)
30-cm plastic scale 1 mm (or 0.1 cm)
Tailor's flexible measuring tape 1 mm
Wooden/Metal metre scale 1 mm

Question 5. Suppose the distance between your school and home is 1.5 km. Express it in metres.

Answer:

  • We know that 1 km = 1000 m.
  • Distance = 1.5 × 1000 m = 1500 m.
  • Answer: The distance between school and home is 1500 metres.

Question 6. Take a tumbler or a bottle. Measure the length of the curved part of the base of glass or bottle and record it.

Answer:

  • Method: A rigid scale cannot measure a curved line directly. Wrap a flexible thread or tailor's measuring tape around the curved base of the tumbler/bottle. Mark the meeting point on the thread, straighten it, and measure its length against a 15-cm or metre scale.
  • Example Observation: Length of the curved base = 22 cm.

Question 7. Measure the height of your friend and express it in (i) metres (ii) centimetres and (iii) millimetres.

Answer (Example height of a friend = 140 cm):

  • In centimetres (cm): 140 cm
  • In metres (m): 140 / 100 = 1.40 m (since 1 m = 100 cm)
  • In millimetres (mm): 140 × 10 = 1400 mm (since 1 cm = 10 mm)

Question 8. 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:

  • Estimation: Approx. 10 coins.
  • Verification:
    • Length of the chosen side of notebook = 20 cm.
    • Diameter (size) of one coin = 2 cm.
    • Number of coins required = Length of notebook / Diameter of coin = 20 / 2 = 10 coins.
  • Conclusion: The estimated number matches the calculated value.

Question 9. Give two examples each for linear, circular and oscillatory motion.

Answer:

  • Linear Motion (objects moving along a straight line):
    • A car moving on a straight road.
    • An apple or fruit falling straight down from a tree.
  • Circular Motion (objects moving along a circular path):
    • Blades of a rotating ceiling fan.
    • A child sitting on a merry-go-round.
  • Oscillatory Motion (objects moving to and fro about a fixed position):
    • Motion of a swing in a park.
    • Motion of a clock's pendulum.

Question 10. 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 Table 5.6.

Answer (Table 5.6):

Category Objects
mm 1. Thickness of a coin, 2. Thickness of a notebook page, 3. Diameter of a pencil lead
cm 1. Length of a pencil, 2. Length of an eraser, 3. Length of a mobile phone
m 1. Length of a classroom, 2. Length of a school playground, 3. Length of a cloth piece / saree

Question 11. 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:

  • Portion A to B (Straight slope downwards): Linear motion (moving along a straight path).
  • Portion B to C (Circular loop): Circular motion (moving along a circular loop).
  • Portion C to D (Straight horizontal path): Linear motion.
  • Portion D to E (Curved loop/path): Circular / Curved motion.
  • Portion E to F (Straight exit path): Linear motion.

Question 12. 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?

  • Materials she should NOT use: Stretchable rubber and cloth.
  • Reason: Stretchable rubber stretches easily when pulled, which alters the distance between markings and gives inaccurate, variable readings. Cloth can also stretch or fold easily. A standard scale requires a rigid, non-stretchable material like plywood or steel to maintain fixed, uniform divisions.

Question 13. Think, design and develop a card game on conversion of units of length to play with your friends.

Answer (Game Design):

  • Set A (Question Cards): Cards with values in different units (e.g., 2 km, 500 cm, 3 m, 40 mm).
  • Set B (Conversion Answer Cards): Cards with equivalent values (e.g., 2000 m, 5 m, 300 cm, 4 cm).
  • Rules: Shuffle both sets and place them face down. Each player turns over two cards. If the two values represent an exact unit conversion (e.g., 2 km = 2000 m), the player keeps the pair. The player with the most pairs wins.

🔬 “Learning further” (Projects & Field Activities)

Measuring Thickness of a Single Page:

  • Measure the total thickness of 100 pages (50 sheets) of a textbook tightly pressed using a scale (e.g., total thickness = 5 mm).
  • Thickness of 1 page: Total Thickness / Number of Pages = 5 mm / 100 = 0.05 mm.

Measuring Leaves of the Same Tree:

  • Collect 5 fallen leaves from the same tree (e.g., Neem or Peepal) and measure their length and breadth using a 15-cm scale.
  • Reason for variation: Leaves vary in size depending on their age/stage of growth, position on the branch, and the amount of sunlight and nutrients received.

Ancient Indian Measurement Units:

  • Units like Angula (finger width), Dhanusa, and Yojana were used in ancient India. Excavated sites of the Harappan Civilisation revealed precise scales with ruled markings made of ivory and bronze.

Jones Counter on Bicycles:

  • A Jones Counter attached to a bicycle wheel counts the number of revolutions. Multiplying the wheel's circumference by the number of turns measures exact distances traveled, commonly used in marathon and road-running races.
💡 Teacher's Tip: Note down all these answers cleanly in your Science notebook. Always keep your eye directly above the scale marking while measuring to avoid parallax error! 📏📐

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