Unable to AddForce on a game object containing a RigidBody2D and a HingeJoint2D?

I have a game object which contains a HingeJoint2D and a RigidBody2D. I’ve also attached the following debugging script:

void FixedUpdate() {
  if (Input.GetKey(KeyCode.Space)) {
    GetComponent<Rigidbody2D>().AddForce(Vector2.up * 100f);

I’ve found that when I have the HingeJoint2D enabled, the script does not add force to the RigidBody2D. However, if I disable the HingeJoint2D, the script adds the force as expected.

Why is this?

What is the HingeJoint2D.connectedBody set to? If it’s not set to anything then you’re asking that its connected to the world. The Rigidbody2D therefore cannot move as you’ve just asked it to rotate around that world point.