Assertion : When a bullet is fired from a gun the bullet pierces a wooden block and stops. The temperature of the bullet and the surrounding layers of wood changes.
Reason : Temperature is related to the energy of motion of the bullet as a whole.

Options

A. Both assertion and reason are true and reason is the correct explanation of assertion
B. Both assertion and reason are true but reason is not the correct explanation of assertion
C. Assertion is true but reason is false
D. Both assertion and reason are false.

Explanation

To solve the question, we need to analyze both the assertion and the reason provided.

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that when a bullet is fired from a gun and pierces a wooden block, the temperature of both the bullet and the surrounding layers of wood changes.
- When the bullet strikes the wooden block, it has kinetic energy due to its motion. As it penetrates the wood, this kinetic energy is converted into other forms of energy, primarily heat.

2. **Kinetic Energy and Heat Generation**:
- The bullet has an initial kinetic energy given by the formula \( KE = \frac{1}{2} mv^2 \), where \( m \) is the mass of the bullet and \( v \) is its velocity.
- As the bullet penetrates the wood, it slows down, meaning its kinetic energy decreases. This loss of kinetic energy is transformed into thermal energy (heat) due to friction and deformation.

3. **Temperature Change**:
- The heat generated from the kinetic energy loss raises the temperature of both the bullet and the surrounding wood.
- Therefore, the assertion that the temperature of the bullet and the surrounding layers of wood changes is correct.

4. **Understanding the Reason**:
- The reason states that temperature is related to the energy of motion of the bullet as a whole.
- While it is true that temperature is related to energy, in this context, the relevant factor is the change in kinetic energy as the bullet penetrates the wood, not the total kinetic energy of the bullet.

5. **Conclusion**:
- The assertion is true because the temperature of the bullet and wood does change due to the conversion of kinetic energy to heat.
- The reason is false because it incorrectly states that temperature is related to the energy of motion of the bullet as a whole, rather than focusing on the change in energy during the impact.

### Final Answer:
- The assertion is true, but the reason is false. Thus, the correct option is C.

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