矢のセットアップ

矢にRigidbodyコンポーネントを追加し、Use Gravity のチェックを外す
Capsule Collider を追加し、Radius=0.03、Height=0.8、Is Trigger にチェックを付ける

矢の機能を呈するスクリプト Arrow.cs を作成し、Arrow にアタッチ


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

public class Arrow : MonoBehaviour
{
  	public float groundSpeed=7.5f;//馬の速度
	public float launchSpeed=10f;
	public float magnify=2f;

	bool flying=false;

	float launched;    
	public void Ready(){
		transform.parent=GameObject.Find("Bow").transform;
		transform.localPosition=new Vector3(0, 0, -0.3f);
		transform.localRotation=Quaternion.Euler(90f, 0f, 0f);
		transform.localScale=new Vector3(1f, 1f, 1f);
		GetComponent<Rigidbody>().velocity=Vector3.zero;
		flying=false;
	}

	public void Fire(){
		transform.parent=null;
		GetComponent<Rigidbody>().velocity=Vector3.forward*groundSpeed + transform.up*launchSpeed;
		launched=Time.time;
		flying=true;
	}

	void Update()
	{
		if(flying){
			var flyingTime=Time.time-launched;
			if(flyingTime>3f){
				Ready();
			}else{
				var scale = 1f + magnify*flyingTime;
				transform.localScale=new Vector3(scale, scale, scale);
			}
		}
	}
}

Main.cs の Update()、OnActivate() に以下のスクリプトを追記


	void Update()
	{
		float d=Vector3.Distance(leftHand.position, rightHand.position);
		Debug.Log(d);
		switch(state){
			case State.Idle:
				if(d<0.4f) state=State.Pull;
				break;
			case State.Pull:
				if(d>0.4f){
					GameObject.Find("Bow").GetComponent<Animation>().Play("BowPullAnimation");
					GameObject.Find("Arrow").GetComponent<Arrow>().Ready();
					state=State.Ready;
				}
				break;
		}
	}

	void OnActivate(InputAction.CallbackContext context){
		if(state==State.Ready){
			GameObject.Find("Bow").GetComponent<Animation>().Play("BowReleaseAnimation");
			GameObject.Find("Arrow").GetComponent<Arrow>().Fire();
			state=State.Idle;
		}
	}