A body moves on a straight line with a uniform velocity Its angular momentum

Options

A. is zero about a point on the straight line.
B. remains constant about any given point.
C. is always zero.
D. is not zero about a point away from the straight line.

Answer

To solve the problem of determining the angular momentum of a body moving in a straight line with uniform velocity, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Angular Momentum**:
Angular momentum (L) of a body about a point is given by the formula:
\[ L = r \times p \]
where \( r \) is the position vector from the point to the mass, and \( p \) is the linear momentum of the body.

2. **Define Linear Momentum**:
The linear momentum \( p \) of the body is given by:
\[ p = mv \]
where \( m \) is the mass of the body and \( v \) is its velocity.

3. **Identify the Perpendicular Distance (r)**:
The value of \( r \) is the perpendicular distance from the point about which we are calculating the angular momentum to the line of motion of the body.

4. **Case 1: Point on the Straight Line**:
If the point is located on the straight line along which the body is moving, the perpendicular distance \( r \) will be zero. Therefore, the angular momentum will be:
\[ L = r \times p = 0 \times mv = 0 \]
Thus, the angular momentum about a point on the straight line is **0**.

5. **Case 2: Point Away from the Straight Line**:
If the point is located away from the straight line, the perpendicular distance \( r \) will be non-zero. In this case, the angular momentum can be calculated as:
\[ L = r \times mv \]
Since both \( m \) and \( v \) are constants (given uniform motion), the angular momentum will remain constant as long as the perpendicular distance \( r \) remains unchanged.

6. **Conclusion**:
- **Option 1**: Angular momentum is **0** about a point on the straight line (True).
- **Option 2**: Angular momentum remains constant about a given point away from the line (True).
- **Option 3**: Angular momentum is **not always 0**; it is only 0 when the point is on the line (False).
- **Option 4**: Angular momentum is **not 0** about a point away from the straight line (True).

### Final Answer:
The correct options are **1, 2, and 4**.