CBSE Class 4 Mathematics NCERT Solutions: Unit 12 How Heavy How Light

To find the total weight of the load, we first calculate the total weight of each type of item and then sum them up.

1. Sacks of wheat: There are 5 sacks, and each weighs 100 kg.

Total weight = 5 \times 100 = 500 \text{ kg}

2. Sacks of rice: There are 3 sacks, and each weighs 35 kg.

Total weight = 3 \times 35 = 105 \text{ kg}

3. Water tank: There is 1 water tank, weighing 50 kg.

Total weight = 1 \times 50 = 50 \text{ kg}

4. Almirah: There is 1 almirah, weighing 70 kg.

Total weight = 1 \times 70 = 70 \text{ kg}

5. Tables: There are 3 tables, and each weighs 10 kg.

Total weight = 3 \times 10 = 30 \text{ kg}

6. Chairs: There are 4 chairs, and each weighs 5 kg.

Total weight = 4 \times 5 = 20 \text{ kg}

7. Mattresses: There are 2 mattresses, and each weighs 20 kg.

Total weight = 2 \times 20 = 40 \text{ kg}

8. Bamboo ladder: There is 1 bamboo ladder, weighing 10 kg.

Total weight = 1 \times 10 = 10 \text{ kg}

9. Pots and pans: The weight is given as 10 kg.

Total weight = 10 \text{ kg}

Now, we add the total weights of all the items to find the total weight of the load:

Total weight = 500 + 105 + 50 + 70 + 30 + 20 + 40 + 10 + 10 \text{ kg}

Total weight = 835 \text{ kg}

The total weight loaded on the cart is 835 kg.

The current total weight of the load is 835 kg. The desired maximum weight is 700 kg. To find out how much weight needs to be removed, we subtract the desired weight from the current weight.

Weight to be removed = Current weight - Desired weight

Weight to be removed = $835\; \backslash text\{\; kg\}\; -\; 700\; \backslash text\{\; kg\}\; =\; 135\; \backslash text\{\; kg\}$

Now, we need to identify items from the list whose combined weight is 135 kg. Let's look at the weights of some items:

• 3 sacks of rice weigh $3\; \backslash times\; 35\; =\; 105\; \backslash text\{\; kg\}$.
• Three tables weigh $3\; \backslash times\; 10\; =\; 30\; \backslash text\{\; kg\}$.

If we remove these items (3 sacks of rice and 3 tables), the total weight removed is:

Total weight removed = $105\; \backslash text\{\; kg\}\; +\; 30\; \backslash text\{\; kg\}\; =\; 135\; \backslash text\{\; kg\}$

Therefore, if Jaiju and Mannu remove 3 sacks of rice and three tables, the weight of the load will become 700 kg, which is not more than the desired limit.

To make a simple balance, you can follow these steps:

1. Take a strong, straight stick of a suitable length. This will be the beam of the balance.
2. Get two identical pans or small containers.
3. Tie each pan securely to one end of the stick using strong thread or string. Ensure the pans hang freely.
4. Find the exact middle point of the stick. Make a small hole or attachment point at this center.
5. Tie another piece of thread to this center point. This thread will be used to hold the balance so that the beam can move freely.
6. Hold the top thread, and the stick should balance horizontally. If it doesn't, adjust the position of the pans or the center point until it balances.

Your balance is now ready to compare the weights of different objects. You can place one object in each pan and observe which pan goes down.

The pan that contains the geometry box will go down.

Reason: A geometry box typically contains multiple items like rulers, compasses, protractors, erasers, etc., making it significantly heavier than a single pencil. When placed on a balance, the object with greater mass (and therefore greater weight) will cause its pan to move downwards.

(Note: A drawing would be included here showing a balance with a pencil in one pan and a geometry box in the other, with the geometry box pan lower.)

Here are some examples of pairs and the results from using a balance:

• Pair: Socks and trouser. Guess: Trouser will be heavier. Check: Trouser is heavier.
• Pair: Toothbrush and toothpaste. Guess: Toothpaste might be heavier. Check: Toothpaste is heavier (usually a full tube is heavier than a toothbrush).
• Pair: Glass and spoon. Guess: Glass will be heavier. Check: Glass is heavier.
• Pair: Dictionary and notebook. Guess: Dictionary will be heavier. Check: Dictionary is heavier.

This activity helps in developing an intuitive understanding of weight comparison.

Using a balance, we can compare three items and arrange them by weight. Here are five examples completed in the table format:

Lightest | In-between weight | Heaviest

------- | -------- | --------

Paper | Eraser | Ball

Notebook | Book | Dictionary

Toothbrush | Toothpaste | Laptop

Orange | Coconut | Pumpkin

Napkin | Handkerchief | Shirt

To complete this, you would first compare two items (e.g., paper and eraser) to find the lighter one. Then, compare the lighter item with the third item (e.g., paper and ball) to find the lightest overall. Repeat comparisons to determine the middle and heaviest items.

No, you cannot accurately find your own weight using the simple balance described in the activity. This type of balance is suitable for comparing the weights of small, everyday objects that can fit into the pans. To measure a person's weight, a much larger and more robust weighing scale (like a bathroom scale) is required, which uses springs or electronic sensors to measure heavier loads accurately.