Deteriorating force on object?

Making a game where the character moves a certain amount away from wherever I click. I wanted to use a deteriorating force to make it feel like the character is getting knocked back, almost exploding the opposite direction of the click. I've already set everything up, and tried using rb2d.AddForce, but the character just moves at a constant speed instead of slowing to a stop after a little bit. I'm just wondering if there is something in the Unity API to allow this, or if I have to manually script the countering velocity.