x=x+v

v=v+gr

cc.Class({

    extends: cc.Component,

    properties: {

        velocity:{

            default:null

        },

        grivatity:{

            default:null

        },

    },

    // use this for initialization

    onLoad: function () {

        this.velocity=30;

        this.grivatity=-1;

    },

    // called every frame, uncomment this function to activate update callback

    update: function (dt) {

        var now=this.node.position

        if(now.y<-250)

        {

            this.velocity=30;

        }

        now.y+=this.velocity;

        this.velocity+=this.grivatity;

        this.node.position=now;

    },

});