Problem With my Physics Cube

Hello everyone!

Well I have a problem with my cube, it has Simulate Physics Enable, also Gravity and its Mass in Kg too (15kg), And everything works as it should, but when I rotate the cube the add impulse through the X axis doesnt work as it should, instead it adds impulse throug the Y axis, or into the wrong direction, depending the rotation.
How can I add impulse only through the X axis no matter the rotation.?