Final answer:
A sundial's time reading can differ due to longitudinal differences, and the shadow length also varies with latitude, meaning a sundial 100 miles north would not read the same time and would cast a shadow of a different length.
Step-by-step explanation:
The time indicated by a sundial does not depend solely on the North-South position but also on the longitudinal difference from the standard time meridian of the time zone. This means that a sundial 100 miles directly north would not necessarily show the same time due to this longitudinal difference. Additionally, the shadow length cast by the gnomon of the sundial would be affected by the local latitude; as you move further from the equator, the angle at which the Sun strikes the Earth changes, thus altering the length of the shadow.
Therefore, while the sundial 100 miles north would still correctly indicate noon when its shadow points due north, throughout the rest of the day, the two sundials would likely show slightly different times and produce shadows of different lengths due to the variation in longitude and the corresponding angle of the sun's rays.