a code sample for https://medium.com/scry-llc/applying-explosion-knock-back-1f394f7160e8

Explosion Example.cs

float desiredMagnitudeToEndForceAnimation = .1f;

IEnumerator AnimateForce(float force, Vector3 forcePosition, float radius)
{
    var rb = GetComponent<Rigidbody>();
    rb.constraints = RigidbodyConstraints.None;
    rb.AddExplosionForce(force, forcePosition, radius);
    do
    {
        yield return new WaitForSeconds(.1f);
    }
    while (rb.velocity.magnitude > desiredMagnitudeToEndForceAnimation  && rb.angularVelocity.magnitude > desiredMagnitudeToEndForceAnimation);

    // It could have been destroyed at any point in time in our waiting
    if(rb != null)
    {
         rb.constraints = RigidbodyConstraints.FreezeAll;
    }

}

public void AddExplosionForce(float force, Vector3 forcePosition, float radius)
{
    StartCoroutine(AnimateForce(force, forcePosition, radius));
}