Which of the following is not a unit of energy?

Options

A. `W-s`
B. kg-m/sec
C. N-m
D. Joule

Explanation

To determine which of the following is not a unit of energy, we will analyze each option one by one.

### Step 1: Analyze the first option - Watt into second
- **Watt (W)** is defined as one joule per second (1 W = 1 J/s).
- Therefore, when we multiply watt by time (in seconds), we get:
\[ \text{Energy} = \text{Power} \times \text{Time} = \text{Watt} \times \text{Second} = (1 \, \text{J/s}) \times (1 \, \text{s}) = 1 \, \text{J} \]
- Thus, **Watt into second is a unit of energy**.

### Step 2: Analyze the second option - kg into meter per second
- The expression \( \text{kg} \times \text{m/s} \) represents momentum, where:
\[ \text{Momentum} = \text{Mass} \times \text{Velocity} = \text{kg} \times \text{m/s} \]
- Since momentum is not a unit of energy, **this option is not a unit of energy**.

### Step 3: Analyze the third option - Newton into meter
- The unit Newton (N) is defined as:
\[ 1 \, \text{N} = 1 \, \text{kg} \cdot \text{m/s}^2 \]
- Work done (or energy) is calculated as:
\[ \text{Work} = \text{Force} \times \text{Displacement} = \text{N} \times \text{m} \]
- Therefore, \( \text{N} \times \text{m} \) is indeed a unit of energy (specifically, it is equal to joules).

### Step 4: Analyze the fourth option - Joule
- The joule (J) is the standard unit of energy in the International System of Units (SI).
- It is defined as the amount of energy transferred when a force of one newton is applied over a distance of one meter.
- Thus, **joule is a unit of energy**.

### Conclusion
After analyzing all the options, we find that the second option, **kg into meter per second**, is not a unit of energy.

### Final Answer:
The option that is not a unit of energy is **kg into meter per second**.

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