PlayerMovement.cs

using UnityEngine;
using System.Collections;

public class PlayerMovement : MonoBehaviour
{
    public float speed;
    private Rigidbody2D rigidbody;

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

    void Update()
    {
        Movement();
    }

    void Movement()
    {
        if (Input.GetKey(KeyCode.A))
        {
            transform.Translate(-speed * Time.deltaTime, 0, 0);
        }
        else if (Input.GetKey(KeyCode.D))
        {
            transform.Translate(speed * Time.deltaTime, 0, 0);
        }
    }

    void OnCollisionEnter2D(Collision2D other)
    {
        if (other.gameObject.tag == "Platform")
        {
            rigidbody.AddForce(new Vector2(0f, 500f));
        }
    }
}