The magnitude of the velocity of the image relative to the man normal to the mirror will be equal to the magnitude of the man's velocity.

Explanation:

When a man moves towards a plane mirror, the mirror reflects the light rays coming from the man and creates an image of the man behind the mirror. To understand the velocity of the image relative to the man, let's break down the scenario step by step.

1. Man's Velocity:
The man is moving towards the mirror with a velocity v. This velocity can be decomposed into two components:
- A component parallel to the mirror's surface.
- A component perpendicular to the mirror's surface.

2. Reflection of Light:
When the light rays coming from the man reach the mirror, they obey the law of reflection. The incident angle of the light rays with respect to the normal to the mirror is equal to the angle of reflection.

3. Formation of Image:
The mirror reflects the light rays and forms an image of the man behind the mirror. The image appears to be at the same distance behind the mirror as the man is in front of the mirror. The image is formed by extending the reflected rays behind the mirror.

4. Relative Velocity of Image:
Since the image is formed by the reflected rays, the velocity of the image will be equal to the velocity of these reflected rays. The direction of the reflected rays is opposite to the direction of the incident rays. Therefore, the image velocity will also be in the opposite direction to the man's velocity.

5. Velocity of Image Relative to the Man:
To determine the magnitude of the velocity of the image relative to the man normal to the mirror, we only need to consider the component of the image velocity that is perpendicular to the mirror's surface. This perpendicular component will be equal to the perpendicular component of the man's velocity.

Conclusion:
In conclusion, the magnitude of the velocity of the image relative to the man normal to the mirror will be equal to the magnitude of the man's velocity. This is because the perpendicular component of the man's velocity is conserved during reflection, resulting in the same magnitude for the image velocity.