Define linear momentum and state its S.I. unit.

Explanation

### Step-by-Step Solution:

1. **Understanding Linear Momentum**:
- Linear momentum is a physical quantity that describes the motion of an object. It is dependent on two factors: the mass of the object and its velocity.

2. **Defining Linear Momentum**:
- Linear momentum (denoted as \( P \)) is defined mathematically as:
\[
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