A body is under the action of two mutually perpendicular forces of 3 N and 4 N. The resultant force acting on the body is

Options

A. 7 N
B. 1 N
C. 5 N
D. zero

Explanation

To find the resultant force acting on a body under the action of two mutually perpendicular forces of 3 N and 4 N, we can use the Pythagorean theorem, as the forces form a right triangle.

### Step-by-Step Solution:

1. **Identify the Forces**:
- Let \( F_1 = 3 \, \text{N} \) (first force)
- Let \( F_2 = 4 \, \text{N} \) (second force)

2. **Determine the Angle Between Forces**:
- The forces are mutually perpendicular, which means the angle \( \theta = 90^\circ \).

3. **Use the Pythagorean Theorem**:
- The magnitude of the resultant force \( R \) can be calculated using the formula:
\[ R = \sqrt{F_1^2 + F_2^2} \]

4. **Substitute the Values**:
- Substitute the values of \( F_1 \) and \( F_2 \):
\[ R = \sqrt{(3 \, \text{N})^2 + (4 \, \text{N})^2} \]

5. **Calculate the Squares**:
- Calculate \( (3 \, \text{N})^2 = 9 \, \text{N}^2 \)
- Calculate \( (4 \, \text{N})^2 = 16 \, \text{N}^2 \)

6. **Add the Squares**:
- Add the results:
\[ R = \sqrt{9 \, \text{N}^2 + 16 \, \text{N}^2} = \sqrt{25 \, \text{N}^2} \]

7. **Take the Square Root**:
- Finally, take the square root:
\[ R = 5 \, \text{N} \]

### Conclusion:
The resultant force acting on the body is \( 5 \, \text{N} \).