Thread: Swing timer, falling object

I'm trying to simulate a falling object with an initial horizontal speed. I understand how to make it move horizontally (no acceleration) but I have some trouble making it move vertically because of the equation y = gt^2/2 + vt + y0. I have problems because of the quadratic equation.

What I tried to do is to do make a time variable which would increase by one every time the action is performed by the SwingTimer. So that I would actually have a timevariable. But I don't think that is the best way to do it?

Can somebody push me in the right direction?

Below you can find the code I have already written:

public class Simulation extends JPanel implements ActionListener
    {
    Timer timer = new Timer(5,this);;
    private int Xpos=0, Ypos=0, velX, velY;
    private int Px,Py;
 
    JButton dropknop;
    private boolean drop = false;
 
    public Simulation()
    {
        this.setBackground(Color.white);
        velX = 2;
        velY = 2;
 
        dropknop = new JButton("DROP");
        dropknop.addActionListener(this);
        this.add(dropknop);
    }
    public int getXpos() {
        return Xpos;
    }
 
    public void paintComponent(Graphics g)
    {
        super.paintComponent(g);
        g.drawRect(Xpos, 0, 20, 20);
 
        if(drop)
        {
            g.fillRect(Px, Py, 5, 5);
        }
    }
 
    public void actionPerformed(ActionEvent ae) 
    {
        if(ae.getSource() == dropknop)
        {
            Px = getXpos();
            this.drop = true;
        }
        if(Xpos<0 || Xpos>986)
        {
            velX = -velX;
        }
        if(Ypos<0 || Ypos>708)
        {
            velY = - velY;
        }
 
        if(drop)
        {
            Px += velY;
            Py += velX;
        }
 
        Ypos += velY;
        Xpos += velX;
        repaint();
    }
}

Thank you in advance!