Final answer:
The Kuiper Belt is flat due to gravitational interactions with Neptune, while the Oort Cloud is spherical due to the gravitational pull of other stars and the Sun.
Step-by-step explanation:
The reason why the Kuiper Belt is flat and the Oort Cloud is spherical is due to different factors.
Firstly, the Kuiper Belt is relatively closer to the Sun compared to the Oort Cloud. This proximity to the Sun causes the gravitational interactions with Neptune to flatten the Kuiper Belt over time. These gravitational interactions influence the orbits of the objects in the Kuiper Belt, causing it to become flat.
On the other hand, the Oort Cloud is influenced by the gravitational pull of other stars as well as the Sun. This gravitational influence from multiple sources causes the Oort Cloud to form a spherical shape.