Unity rigidbody2D with Vector3

Hi,
I’m trying to make repel function(2D platform).
I found this code below in the sample project of unity2D

Vector3 hurtVector = transform.position - enemy.position + Vector3.up * 5f;
rigidbody2D.AddForce(hurtVector * hurtForce);

So I just removed “+ Vector3.up * 5f;” part and thought it would work.
But it didn’t work as I expected.
So I tested several Vector3 to see how things work.

Vector3(0, 1, 0) worked fined. My object moved up as expected.
However, Vector3(1, 0, 0) and Vector3(0, 0, 1) didn’t work as I expected.
My object didn’t move forward nor right, only slightly dragged along with ground.

Why would only y-axis work fine and x,z-axis not?

Where have I gone wrong?
Is there any solution?

I have half of the answer. 2d “don’t have” the Z axis, so don’t expect movement back and forward.