If you took a 20-foot tree and hammered a spike into it 3-feet above the ground, how high would that spike be 30 years later when the tree is 100 feet tall? and why?

The spike will remain at 3-feet above the ground in 30 years time because the spike does not increase in height as the tree does.

Please find the explanation below

Explanation:

Living things including the trees stated in this question are capable of growth (in height and girth). According to this question, a spike is hammered into a tree base at 3-feet above the ground level. However, after 30 years, the tree grows to 100 feet but the spike will remain at 3-feet above the ground.

This is because the spike, which is naturally incapable of growth, will not grow alongside the tree. A plant (tree) undergoes growth at its apices or meristem i.e. the tree will elongate from the tip and not any other part. Hence, the tree will grow and leave the spike at its initial level.