OnCollisionEnter not called

Hi,I new in Unity,I have a question when I use 2dtoolkit:
Add two sprite on screen,they all have “Box collider 2d”,“rigidbody 2d” component.when start the game,move one of them through rigidbody2D.AddForce() in a script,this script also have function void OnCollisionEnter(Collision collisionInfo),and these two sprite have collision effect,but not call OnCollisionEnter().I confuse.
Thank you to read and have some ideas for me.

void OnCollisionEnter —> void OnCollisionEnter2D

So remember about “2D” in the void xxxxx2D