-bash: sudo: command not found

This generally means you have managed to mess up your PATH environment variable.

To execute your command you could use

/usr/bin/sudo /usr/sbin/diskutil unmountDisk force /dev/disk1

This is a short term solution.

Chances are you have one of the following shell initialization files and it has a broken export PATH

.bash_profile

.bash_login

.profile

.bashrc

Use this command to see if you have any of these files:

cd $HOME

/bin/ls .bash_profile .bash_login .profile .bashrc

By default none of these files exist in your home directory.

If you have one of these files you can edit it using

/usr/bin/nano .name_of_file

Or use a GUI based text editor, such as TextWrangler

<http://www.barebones.com/products/textwrangler/>

You should either fix PATH modification, or remove the broken PATH modification

After making a change to your shell initialization file, you should quit the Terminal session and start a new one so that the modified shell initialization file is re-loaded into the shell.

You could also rename the broken shell initialization file and fix it later.

/bin/mv .name_of_file saved.name_of_file

Or you can just delete it

/bin/rm .name_of_file

Again, quit and start a new Terminal session.

please provide the output from

echo $PATH

And please copy and paste the command you entered and the error output.