Users belong to the whole database; but not to a particular tablespace.

If you want to drop the user along with his associated objects and foreign keys that depend on the tables owned by the user;

then u have to say

SQL>DROP USER SCOTT CASCADE;


If u say,
SQL>Drop tablespace TBS including contents;
This will drop all the objects in the tablespace, no matter who is owning the objects.

Well with the imp command, the object owned by SAM in the art.dmp will be imported into the TOM schema in the target database. Well the user TOM has to be present in advance for this.