A grinding wheel in the shape of a solid disk is 0.210 m in diameter and has a mass of 2.50 kg. The wheel is rotating at 2500 rpm about an axis through its center. a) What is its kinetic energy? (in J)
b) How far would it have to drop in free fall to acquire the same amount of kinetic energy? (h=___m)

I'm thinking it's 2 you are asked to explain the earth's magnetic field. which is the best reply? 1. the earth's magnetic south is similar to the north pole of a magnet. 2. the earth's core has a strong magnetic charge similar to the south pole of a magnet. 3. the earth's geomagnetic south is similar to the south pole of a magnet. 4. the earth's magnetic charge is not centered at either pole; it varies based on location.