Auniform solid sphere of radius r = 3.5 km produces a gravitational acceleration of ag on its surface. at what distance from the sphere's center are there points (a) inside and (b) outside the sphere where the gravitational acceleration is ag/ 5?

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.