Top down game in Unity. Player can't stop moving

Question

i've following issue. I'm trying to make game with top down view (something like first GTA game). The problem is when i press the key my player is moving, but can't stop. Here you can see my script:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class PlayerMovemenet : MonoBehaviour
{
    private Rigidbody2D m_Rigidbody;
    private Transform playerTransform;
    public float m_Speed = 100.0f;
  

    // Start is called before the first frame update

    void Start()
    {
        m_Rigidbody = GetComponent<Rigidbody2D>();
        playerTransform = GameObject.Find("Player").transform;
        
    }

    // Update is called once per frame
    void FixedUpdate()
    {

        Vector3 playerPos = playerTransform.eulerAngles;

        if (Input.GetKey(KeyCode.UpArrow))
        {   
            m_Rigidbody.velocity= transform.up * Time.deltaTime * m_Speed;
            
        }



            if (Input.GetKey(KeyCode.DownArrow))
            {
                
                m_Rigidbody.velocity = transform.up * Time.deltaTime * (-m_Speed);
            
            }



            if (Input.GetKey(KeyCode.RightArrow))
            {
                 transform.Rotate(0, 0, -1 * m_Speed * Time.deltaTime);
            }

        if (Input.GetKey(KeyCode.LeftArrow))
        {
            transform.Rotate(0, 0, 1 * m_Speed * Time.deltaTime);

        }
        }


    }

'''

Can you please tell me how to fix it? Thanks for your answers.

Answer 1

Note that in general a velocity already is a value in absolute units per second and you don't want to multiply by Time.deltaTime in that case.

Also in general whenever dealing with Physics I wouldn't use transform at all but rather do everything via the Rigidbody.

And then simply when you don't press a key do

if (Input.GetKey(KeyCode.UpArrow))
{   
    m_Rigidbody.velocity = Quaternion.Euler(0, 0, m_Rigidbody.rotation) * Vector3.up * m_Speed;
}
else if (Input.GetKey(KeyCode.DownArrow))
{           
    m_Rigidbody.velocity = Quaternion.Euler(0, 0, m_Rigidbody.rotation) * Vector3.down * m_Speed;
}
else
{
    m_Rigidbody.velocity = Vector2.zero;
}

For the rotation I would also rather go

m_Rigidbody.rotation += m_Speed * Time.deltaTime;

and

m_Rigidbody.rotation -= m_Speed * Time.deltaTime;