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Textbook Exercises: Let us Enhance our Learning

January 20, 2025
3 min read
solutions exercises chapter-5

Q1. Match the lengths with suitable units

Column I (Length) vs Column II (Unit)

Column IAnswer (Column II)Reason
Distance between Delhi and LucknowkilometreLarge distance between cities.
Thickness of a coinmillimetreVery small length.
Length of an erasercentimetreSmall object measuring a few cm.
Length of school groundmetreMedium large area, best measured in metres.

Q2. True or False

(i) The motion of a car moving on a straight road is an example of linear motion. Answer: True

(ii) Any object which is changing its position with respect to a reference point with time is said to be in motion. Answer: True

(iii) 1 km = 100 cm. Answer: False Correction: 1 km=1000 m1 \text{ km} = 1000 \text{ m} and 1 m=100 cm1 \text{ m} = 100 \text{ cm}. So, 1 km=100,000 cm1 \text{ km} = 100,000 \text{ cm}.

Q3. Which is NOT a standard unit of measuring length?

(i) millimetre (ii) centimetre (iii) kilometre (iv) handspan

Answer: (iv) handspan Reason: Handspan is a non-standard unit because it varies from person to person.

Q4. Smallest value on different scales

This is an activity-based question. Typical results:

  • 15cm Plastic Scale: The smallest division is usually 1 mm (0.1 cm).
  • Tailor’s Tape: Often marked in inches or cm. Smallest division is usually 1 mm or 1/8 inch.

Q5. Conversion Problem

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

Solution: We know that: 1 km=1000 metres1 \text{ km} = 1000 \text{ metres}

Given distance = 1.5 km1.5 \text{ km}

Distance in metres=1.5×1000=1500 metres\begin{aligned} \text{Distance in metres} &= 1.5 \times 1000 \\ &= 1500 \text{ metres} \end{aligned}

Answer: 1500 m.

Q6 - Q8. Practical Activities

  • Q6 (Curved base): Use a thread to wrap around the base, then measure the thread length on a scale.
  • Q7 (Height): Use a measuring tape.
    • Example: Height = 150 cm.
    • In metres: 1.50 m.
    • In mm: 1500 mm.
  • Q8 (Coin Estimate):
    • Step 1: Place coins edge-to-edge along the notebook side. Count them (e.g., 10 coins).
    • Step 2: Measure notebook side with scale (e.g., 20 cm).
    • Step 3: Measure coin diameter (e.g., 2 cm).
    • Verification: 10 coins×2 cm/coin=20 cm10 \text{ coins} \times 2 \text{ cm/coin} = 20 \text{ cm}. Matches!

Q9. Examples of Motion

  1. Linear Motion:
    • An apple falling from a tree.
    • A striker hitting a coin on a carrom board.
  2. Circular Motion:
    • Tip of the second hand of a clock.
    • A cyclist moving on a circular track.
  3. Oscillatory Motion:
    • Motion of a needle in a sewing machine.
    • Motion of a cradle.

Q10. Sizes of Objects (Table 5.6)

  • mm: Thickness of ID card, tip of pen, ant.
  • cm: Pencil box, water bottle, mobile phone.
  • m: Length of classroom, height of a door, saree length.

Q11. Rollercoaster Track Analysis

Refer to Fig 5.19 in textbook.

  • Section A to B (Straight down): Linear Motion (mostly straight path downwards).
  • Loop (C to D to E): Circular Motion (The ball travels in a circle/loop).
  • Exit (E to F): Linear Motion (Moving straight out).

Q12. Tasneem’s Scale Material

Question: Tasneem wants to make a metre scale. Materials considered: plywood, paper, cloth, stretchable rubber, steel. Which should she NOT use?

Answer: She should not use stretchable rubber (and arguably cloth if it stretches).

Reason: A standard measuring device must have a fixed length. Stretchable rubber changes its length when pulled, so the markings (cm/mm) would expand, giving inaccurate measurements. Plywood and steel are rigid and good for scales.

Q13. Card Game

Activity for students to design cards matching units (e.g., Card A: “1000 m”, Card B: “1 km”).