game object falling through plane when adding rigid body component

Hi all, i am fairly new to unity and am trying to create a tank game. So far i have had no problems creating the tank and plane, and scripting the movement. I am now onto the task of creating a maze environment for the tank to move about, and so am setting the physics for the game. I have added the rigid body component to the tank, so that it is unable to move straight through the maze walls, and have come across my first setback.

When i hit the play button, the tank simply falls through the plane. Before i added the rigid body component to the tank, i was able to move it around the plane using the arrow keys, and it would not fall through.

When i look at the properties of the plane, both mesh collider, and "is trigger" are checked, is this where i am going wrong? As i said this is my first attempt at a game on unity, and so any help would be much appreciated!