Assertion : When two real bodies collide then K.E of the system first decreases and then increases .
Reason : At the time collision bodies are first deformed and then due to elasticity bodies try to reform again.

Options

A. If both assertion and reason are corret and reason is a correct explanation of the assertion .
B. If both assertion and reason are correct but reason is ot the correct explanation of assertion .
C. If assertion is correct but reason is incorrect .
D. If both assertion and reason are incorrect .

Explanation

To solve the question regarding the assertion and reason about the collision of two real bodies, let's break it down step by step:

### Step 1: Understand the Assertion
The assertion states that when two real bodies collide, the kinetic energy (K.E.) of the system first decreases and then increases.

### Step 2: Analyze the Collision Process
When two bodies collide, they undergo deformation. Initially, as they collide, their velocities decrease due to the impact, which leads to a loss of kinetic energy. This energy is not lost but transformed into other forms, primarily potential energy due to deformation.

### Step 3: Kinetic Energy Decrease
During the collision, the kinetic energy of the system decreases because:
- The bodies are compressing and deforming.
- The velocities of the bodies momentarily drop as they reach maximum deformation.

### Step 4: Energy Transformation
As the bodies deform, the kinetic energy is converted into elastic potential energy. This is the energy stored in the bodies due to their deformation.

### Step 5: Kinetic Energy Increase
After the maximum deformation, the bodies begin to return to their original shape due to their elastic properties. As they reform, the stored potential energy is converted back into kinetic energy. However, due to energy losses (like heat and sound), the final kinetic energy after the collision is less than the initial kinetic energy before the collision.

### Step 6: Conclusion on the Assertion
Thus, the assertion is correct: the kinetic energy of the system decreases during the collision and then increases as the bodies return to their original shape.

### Step 7: Understand the Reason
The reason states that during the collision, bodies are first deformed and then, due to elasticity, they try to reform again. This is a correct statement because the process of deformation and subsequent restoration is fundamental to understanding how kinetic energy is transformed during a collision.

### Step 8: Verify the Relationship
Both the assertion and reason are correct, and the reason provides a valid explanation for the assertion. Therefore, the correct answer is that both the assertion and reason are true, and the reason correctly explains the assertion.

### Final Answer
Both the assertion and reason are correct, and the reason is the correct explanation of the assertion.

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