A block of mass 4 kg is suspended through two light spring balances A and B is series. Then A and B will read respectively.

Options

A. `4kg` and zero kg
B. `4 kg` and `4kg`
C. zero kg and 4 kg
D. 2kg and 2kg

Explanation

To solve the problem of determining the readings of the two spring balances A and B when a block of mass 4 kg is suspended through them in series, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Mass and Weight**:
- The mass of the block is given as 4 kg.
- The weight (force due to gravity) can be calculated using the formula:
\[ \text{Weight} = \text{mass} \times g \]
- Here, \( g \) (acceleration due to gravity) is approximately \( 9.8 \, \text{m/s}^2 \).
- Therefore, the weight of the block is:
\[ \text{Weight} = 4 \, \text{kg} \times 9.8 \, \text{m/s}^2 = 39.2 \, \text{N} \]

2. **Understanding the System**:
- The block is suspended, meaning it is in equilibrium. The tension in the spring balances must equal the weight of the block.
- Since the spring balances A and B are in series, the tension in both balances will be the same.

3. **Calculate the Tension**:
- The tension in the system (which is the same for both spring balances) is equal to the weight of the block:
\[ T = 39.2 \, \text{N} \]

4. **Convert Tension to Mass Reading**:
- The spring balances will read the equivalent mass that corresponds to the tension. To find the mass reading, we can use the formula:
\[ \text{Reading (kg)} = \frac{\text{Tension (N)}}{g} \]
- Substituting the values:
\[ \text{Reading} = \frac{39.2 \, \text{N}}{9.8 \, \text{m/s}^2} = 4 \, \text{kg} \]

5. **Conclusion**:
- Therefore, both spring balances A and B will read 4 kg each.

### Final Answer:
- The readings of spring balances A and B are both 4 kg.

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