初速を加えた時に地面に落ちる座標を求めるスクリプト

Test5

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

public class Test5 : MonoBehaviour
{
	//ダミーの球
	[SerializeField]
	private GameObject dummySphere;

	//初速
	[SerializeField]
	private Vector3 v0;

	//地面の座標
	[SerializeField]
	private float gp;

	private Rigidbody rigid;
	private bool isShot = false;
	private float timeCnt = 0.0f;
	private float stopTime = 0.0f;

	void Start()
	{
		rigid = GetComponent<Rigidbody>();
		if (!rigid)
		{
			rigid = gameObject.AddComponent<Rigidbody>();
		}
		rigid.isKinematic = true;
		dummySphere.transform.position = transform.position;
	}

	void Update()
	{
		if (Input.GetKeyDown(KeyCode.Space))
		{
			var t1 = (v0.y + Mathf.Sqrt(Mathf.Pow(-v0.y, 2.0f) + (-2 * -Physics.gravity.y * (-transform.position.y + gp)))) / (-Physics.gravity.y);
			var t2 = (v0.y - Mathf.Sqrt(Mathf.Pow(-v0.y, 2.0f) + (-2 * -Physics.gravity.y * (-transform.position.y + gp)))) / (-Physics.gravity.y);
			Debug.Log("t1:" + t1.ToString("f3") + "     t2:" + t2.ToString("f3"));

			//秒数がNaNの時か秒数がマイナスの時は処理しない
			if ((float.IsNaN(t1) && float.IsNaN(t2)) || (t1 < 0) && (t2 < 0))
				return;

			//地面に落ちるまでの時間
			stopTime = (t1 > 0) ? t1 : t2;

			//地面に落ちる位置
			var pos = new Vector3(v0.x * stopTime, gp, v0.z * stopTime);
			pos.x += transform.position.x;
			pos.z += transform.position.z;

			//ダミーの球を落ちる位置に表示する
			dummySphere.transform.position = pos;

			rigid.isKinematic = false;
			rigid.AddForce(v0, ForceMode.VelocityChange);
			isShot = true;
			timeCnt = 0.0f;
		}

		if (!isShot)
			return;

		timeCnt += Time.deltaTime;
		if (timeCnt >= stopTime)
		{
			isShot = false;
			Debug.Break();
		}
	}
}