How to stop a sphere that is using GetAxis from moving? (Roll-A-Ball Tutorial)

(I just wrote a huge wall of text for like 5 minutes and when I tried to post it, it all was just deleted, so I have to type everything out again, and now it's going to be shorter...)

I am on my second day of learning Unity and are currently doing the roll-a-ball tutorial. I am trying to add a restart button, that teleports the ball back to the start position. It all works good, but the ball will keep moving after I restart, but I want it to stay in a spot and not move by itself.

What I mean is that if I'm moving left at max speed and press 'R' to restart, then it will keep moving left fast for some time.

Here's my code that I just tried out and "hoped" would work, but I think that the problem I have here is that the GetAxis doesn't get restarted, and the next frame after the restart new AxisHorizontal/Vertical values will be assigned and so will AddForce:

 using UnityEngine;
 using System.Collections;
 
 public class PlayerScript : MonoBehaviour {
 
     public float movementSpeed = 7f;
     private Rigidbody rigidSphere;
 
     void Start() {
         rigidSphere = GetComponent<Rigidbody>();
     }
 
     void FixedUpdate() {
         float axisHorizontal = Input.GetAxis("Horizontal");
         float axisVertical = Input.GetAxis("Vertical");
 
         Vector3 movementForce = new Vector3(axisHorizontal, 0.0f, axisVertical);
         rigidSphere.AddForce(movementForce * movementSpeed);
 
         if (Input.GetKeyDown(KeyCode.R)) {
             transform.position = new Vector3(0, 0, 0);
             rigidSphere.AddForce(0, 0, 0);
             axisHorizontal = 0;
             axisVertical = 0;
         }
     }
 }

I tried googling on how to change the value that is taken from GetAxis, but others claim it's impossible to do so. So I have really no idea how to make it not keep moving forever...

And I also got two 'bonus' questions that have arised during those two days that I have been learning Unity, but they are not worth a new thread.

First, how do I make the ball stop moving after some time after I press a button? For example, I press 'W' just for a second, but the ball will keep moving forward forever and will never stop. What I want to achieve is after I for example press 'W' for a second, after a few seconds the ball will completely stop, it just seems that the value from GetAxis never goes back to 0. I tried to google about it, and I think it's something to do with Gravity in the Input Manager - I tried changing it, but no results.

And the second question is how I "pause time" in code, I googled and found out I have to use something like WaitForSeconds() and IEnumerator, but I couldn't do it, the docs didn't help neither.

I'd be really grateful if someone could help me with these problems.