A block of mass 1 kg is placed on a horizontal surface . The reaction force to the weight of the block is

Options

A. The 10 N normal force from the surface
B. The 10 N reaction force from the block of the surface
C. The weight of the earth
D. A 10 N force on earth

Answer

To find the reaction force to the weight of a block of mass 1 kg placed on a horizontal surface, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Weight of the Block**:
The weight (W) of the block can be calculated using the formula:
\[ W = m \cdot g \]
where:
- \( m \) is the mass of the block (1 kg),
- \( g \) is the acceleration due to gravity (approximately \( 10 \, \text{m/s}^2 \) on the surface of the Earth).

2. **Calculate the Weight**:
Substituting the values into the formula:
\[ W = 1 \, \text{kg} \cdot 10 \, \text{m/s}^2 = 10 \, \text{N} \]

3. **Understanding Reaction Force**:
According to Newton's third law of motion, for every action, there is an equal and opposite reaction. The weight of the block acts downward, and the surface exerts an upward force known as the normal force (R), which is the reaction force to the weight.

4. **Set the Reaction Force Equal to the Weight**:
Since the block is in equilibrium (not moving), the normal force (R) is equal to the weight (W):
\[ R = W \]

5. **Final Calculation**:
Therefore, the reaction force to the weight of the block is:
\[ R = 10 \, \text{N} \]

### Conclusion:
The reaction force to the weight of the block is **10 N**.

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