接触したら只管ジャンプするやつ

Jump.cs

using UnityEngine;
using System.Collections;

[RequireComponent(typeof(Rigidbody2D))]
public class Jump : MonoBehaviour {

	[SerializeField, HideInInspector]
	Rigidbody2D rigidbody = null;

	void Reset()
	{
		rigidbody = GetComponent<Rigidbody2D>();
	}

	void Update () 
	{
		var velocity = rigidbody.velocity;
		velocity.x = Input.GetAxis("Horizontal") * 5;
		rigidbody.velocity = velocity;
	}

	void OnCollisionEnter2D(Collision2D coll)
	{
		var velocity = rigidbody.velocity;
		if(velocity.y <= 0 ){
			velocity.y = 6;
			rigidbody.velocity = velocity;
		}
	}
}