simple sping effect

yoyoSpring.js

    var g = 400;
    var h = 10;
    var m = 1;
    var totalTime = 0;
    var engine = m * g * h;
    var t = Math.sqrt((2 * h)/g);
    var vt = 0;
    var v0 = 0;
    function startYoYo(dt)
    {
        if(!startYouYou)
        {
            return;
        }
        var pos = cube.position.clone();
        if(engine <= m * g * h / 8) {
            cube.position.set(pos.x, 0, pos.z)
            console.log(cube.position)
            startYouYou = false;
            return;
        }
        totalTime += dt;
        if(v0 == 0) {
            var s0 = 0.5 * g * totalTime * totalTime;
            var h0 = h - s0;
            cube.position.set(pos.x, h0, pos.z)
            console.log(cube.position)
            if(totalTime >= t)
            {
                // engine -= engine /2;
                engine = engine/2;
                v0 = Math.sqrt(g * h);
                console.log("v0")
                console.log(v0)
                totalTime = 0;
            }
        }
        else {
            var s1 = v0 * totalTime - 0.5 * g * totalTime * totalTime;
            cube.position.set(pos.x, s1, pos.z)
            console.log(cube.position)
            if(s1 <= 0) {
                engine = engine/2;
                v0 = Math.sqrt(g * h/2);
                totalTime = 0;
            }
        }
    }