Bash script and Crontab

There is one thing I want to take note about running a bash script with crontab:

If I use the bash script alone, this will work:

$ /path/to/my/script.sh


#! /bin/bash
export DISPLAY=:0
/path/to/my/pythonGUIapp.py &



But if I run script.sh with crontab, It will not work:

$ sudo crontab -u trinh -e

5 5  * * *  /path/to/my/script.sh


To make it work, I have to change directory to the pythonGUIapp.py before executing it. So, change the script.sh as below:

#! /bin/bash
export DISPLAY=:0
cd /path/to/my/
./pythonGUIapp.py &