A bar magnet of magnetic moment `2.0 A m^2` is free to rotate about a vertical axis through its centre. The magnet is released from rest from the east-west position. Find the kinetic energy of the magnet as it takes the north-south position. The horizontal component of the earth's magnetic field is `B = 25 muT`.

Explanation

To solve the problem, we need to find the kinetic energy of a bar magnet as it rotates from the east-west position to the north-south position. We will use the concepts of magnetic potential energy and kinetic energy in the context of magnetic moments.

### Step-by-Step Solution:

1. **Understanding the Initial and Final Positions**:
- The bar magnet is initially in the east-west position, where its magnetic moment is perpendicular to the horizontal component of the Earth's magnetic field.
- When it rotates to the north-south position, the magnetic moment aligns with the magnetic field.

...