A metal sheet is placed in front of a strong magnetic pole. A force is needed to

Answer

To solve the problem of determining the force needed when a metal sheet is placed in front of a strong magnetic pole, we will analyze each option provided in the question.

### Step-by-Step Solution:

1. **Understanding the Scenario**:
- A metal sheet is placed in front of a strong magnetic pole. We need to consider the properties of the metal sheet (whether it is magnetic or non-magnetic) and how it interacts with the magnetic field.

2. **Analyzing Option 1**:
- **Option**: A force is needed to hold the sheet there if the metal is magnetic.
- **Explanation**: If the metal sheet is magnetic, it will experience a magnetic force due to the magnetic field of the pole. This can either be an attractive or repulsive force depending on the orientation of the magnetic poles. Therefore, to keep the sheet stationary in front of the magnetic pole, a force is indeed needed to counteract this magnetic interaction.
- **Conclusion**: This option is **correct**.

3. **Analyzing Option 2**:
- **Option**: A force is needed to hold the sheet there if the metal is non-magnetic.
- **Explanation**: If the metal sheet is non-magnetic, it does not have its own magnetic field. Therefore, there will be no attraction or repulsion between the non-magnetic sheet and the magnetic pole. As a result, no force is needed to hold the sheet in place.
- **Conclusion**: This option is **not correct**.

4. **Analyzing Option 3**:
- **Option**: A force is needed to move the sheet away from the pole with uniform velocity if the metal is non-magnetic.
- **Explanation**: When the non-magnetic sheet is placed in front of the magnetic pole, it may not be attracted, but if you try to move it away from the pole, you will need to overcome any induced magnetic effects (if any) or the inertia of the sheet. However, in a practical scenario, if the sheet is influenced by the magnetic field, a force will be required to maintain a uniform velocity while moving it away.
- **Conclusion**: This option is **correct**.

### Final Summary:
- **Correct Options**: 1 and 3
- **Incorrect Option**: 2