Which of the following quantities has its unit as newton - second?

Options

A. Energy
B. Torque
C. Momentum
D. Angular momentum

Explanation

To solve the question "Which of the following quantities has its unit as newton-second?", we will analyze each option provided in the question.

### Step-by-Step Solution:

1. **Understanding Units**:
- The unit "newton" (N) is defined as \(1 \, \text{N} = 1 \, \text{kg} \cdot \text{m/s}^2\).
- Therefore, "newton-second" (N·s) can be expressed as \(1 \, \text{N} \cdot 1 \, \text{s} = 1 \, \text{kg} \cdot \text{m/s}^2 \cdot \text{s} = 1 \, \text{kg} \cdot \text{m/s}\).

2. **Analyzing Each Option**:
- **Energy**: The unit of energy is joules (J), which is equivalent to newton-meter (N·m). This does not correspond to newton-second (N·s).
- **Torque**: Torque is defined as force times displacement, which has the unit newton-meter (N·m). Thus, it is not equivalent to newton-second (N·s).
- **Momentum**: Momentum is defined as mass times velocity (p = mv). The unit of momentum is kg·m/s. If we express this in terms of force and time, we can say that momentum can also be represented as force multiplied by time (since force is the rate of change of momentum). Therefore, the unit of momentum can indeed be expressed as newton-second (N·s).
- **Angular Momentum**: Angular momentum is defined as the cross product of the radius vector and momentum (L = r × p). The unit of angular momentum is kg·m²/s, which is not equivalent to newton-second (N·s).

3. **Conclusion**:
- Among the options analyzed, the only quantity that has the unit of newton-second is **momentum**.

### Final Answer:
The quantity that has its unit as newton-second is **momentum**.