Newton's law are valid in

Options

A. any reference frame
B. a frame moving with constant velocity w.r.t. an inertial fame.
C. all reference frames which are at rest w.r.t. an inertial frame.
D. the reference frame attached to the earth.

Answer

To determine where Newton's laws of motion are valid, we need to analyze the given options based on the concept of inertial and non-inertial reference frames.

### Step-by-Step Solution:

1. **Understanding Inertial Frames**:
- Newton's laws of motion are valid only in inertial frames. An inertial frame is one where an object either remains at rest or moves at a constant velocity unless acted upon by a net external force.

2. **Analyzing the Options**:
- **Option 1**: "Any reference frame"
- This option is incorrect because Newton's laws do not apply in non-inertial frames (frames that are accelerating).

- **Option 2**: "A frame moving with constant velocity with respect to an inertial frame"
- This option is correct. A frame moving at a constant velocity is still considered an inertial frame, and thus Newton's laws are valid here.

- **Option 3**: "Reference frames which are at rest with respect to an inertial frame"
- This option is also correct. Frames at rest relative to an inertial frame are inertial frames themselves, so Newton's laws apply.

- **Option 4**: "The reference frame attached to the Earth"
- This option is incorrect. The Earth is not an inertial frame due to its rotation and the presence of gravitational forces acting on it, making it a non-inertial frame.

3. **Conclusion**:
- The correct answers are **Option 2** and **Option 3**. Newton's laws are valid in these frames.

### Summary of Correct Options:
- **Correct Options**: 2 and 3
- **Incorrect Options**: 1 and 4