move object to fixed position (from .x 20 to .x 40) on swipe

I want to move my object a fixed amount to the right/left (on x axis) on swipe. I have my functions to detect swipe, but I don't know a good way to move my object.

This is what I've got so far

 public float speed;
 private Rigidbody2D rb2d;

 void Start(){
     rb2d = GetComponent<Rigidbody2D>();
 }
 // leaving out swipe detection method, not relevant
 public void onLeftSwipe () {
     Vector2 movement = new Vector2(rb2d.position.x -20, rb2d.position.y);
     rb2d.AddForce(movement * speed);
 }

This will add a force to my object, but what I need is to make the object stop when it has reached its destination, which is current position - 20, on left swipe. I don't want to just give it a new position, I must have that feeling of the object traveling there.

I am very new to unity, and c#, so it would be better to give me advice on how to solve it (pointing me to tutorials, docs, examples) rather than providing the solution, if you do have a good solution to share, please explain it also :)