proto_top_down/Assets/Scripts/Projectile.cs

using UnityEngine;

[RequireComponent(typeof(Rigidbody2D))]
public class Projectile : MonoBehaviour
{
    private Transform _transform;
    private Rigidbody2D _rigidbody;
    private float _startTime;

    public float speed = 7;
    public float lifeTime = 5;
    public float damage = 2;
    
    private void Start()
    {
        _transform = transform;
        _rigidbody = GetComponent<Rigidbody2D>();
        _rigidbody.gravityScale = 0;
        _startTime = Time.time;
    }
    
    private void Update()
    {
        _transform.position += _transform.up * (speed * Time.deltaTime);

        if (_startTime + lifeTime < Time.time)
        {
            Destroy(gameObject);
        }
    }

    // TODO: ignore owner
    private void OnCollisionEnter2D(Collision2D collision)
    {
        var health = collision.gameObject.GetComponent<Health>();
        if (health != null)
        {
            health.DealDamage(damage);
        }
    }
}