Solution

src/main/java/lab/App.java

@@ -50,12 +50,15 @@ public class App extends Application {
 	 *@return      nothing
 	 */
 	private void drawScene() {
+		World world = new World(canvas.getWidth(), canvas.getHeight());
 		//graphic context is used for a painting
 		GraphicsContext gc = canvas.getGraphicsContext2D();
 		int timeout = 10;
 		while (!Routines.isEndOfThreadRequestedByJavaVM()) {
+			world.draw(gc);
 			Routines.sleep(timeout);
 			double deltaT = timeout / 1000.;
+			world.simulate(deltaT);
 		}
 	}
 	

src/main/java/lab/Bullet.java

+package lab;
+
+import javafx.geometry.Point2D;
+import javafx.scene.canvas.GraphicsContext;
+import javafx.scene.paint.Color;
+
+public class Bullet {
+
+	private Point2D start;
+	
+	private Point2D position;
+	
+	private Point2D speed;
+	
+	private double size;
+	
+	private World world;
+
+	private Point2D acc;
+
+	public Bullet(World world, Point2D start, Point2D speed, double size) {
+		this.world = world;
+		this.start = start;
+		this.speed = speed;
+		this.size = size;
+		this.position = start;
+		this.acc = new Point2D(0, - World.GRAVITATION_ACCELERATION);
+	}
+
+	
+	public void draw (GraphicsContext gc) {
+		gc.save();
+		gc.setFill(Color.STEELBLUE);
+		Point2D p = world.transform(position);
+		gc.fillOval(p.getX() - size / 2, p.getY() - size / 2, size, size);
+		gc.restore();
+	}
+	
+	public void simulate(double deltaT) {
+		
+		position = position.add(speed.multiply(deltaT));
+		speed = speed.add(acc.multiply(deltaT));
+	}
+	
+}

src/main/java/lab/Canon.java

+package lab;
+
+
+
+import javafx.geometry.Point2D;
+import javafx.scene.canvas.GraphicsContext;
+import javafx.scene.transform.Affine;
+import javafx.scene.transform.Transform;
+
+public class Canon {
+	
+	private int angle;
+	private Point2D position;
+	
+	public void draw(GraphicsContext gc) {
+		gc.save();
+		gc.transform(new Affine(Transform.rotate(angle, position.getX(), position.getY())));
+		gc.fillRect(position.getX(), position.getY(), 40, 20);
+		gc.restore();
+	}
+}

src/main/java/lab/World.java

+package lab;
+
+import javafx.geometry.Point2D;
+import javafx.scene.canvas.GraphicsContext;
+import javafx.scene.paint.Color;
+
+public class World {
+	
+	public static double GRAVITATION_ACCELERATION = 9.81;
+	
+	public double width;
+	
+	public double height;
+	
+	private Bullet bullet;
+
+	private Canon canon; 
+	
+	public World(double width, double height) {
+		this.width = width;
+		this.height = height;
+		this.bullet = new Bullet(this, new Point2D(10, 11), new Point2D(50,30), 10);
+		this.canon = new Canon();
+	}
+	
+	public void draw(GraphicsContext gc) {
+		gc.save();
+		gc.setFill(Color.LIGHTYELLOW);
+		gc.fillRect(0, 0, width, height);
+		gc.restore();
+		this.bullet.draw(gc);
+		this.canon.draw(gc);
+	}
+	
+	public void simulate(double deltaT) {
+		bullet.simulate(deltaT);
+	}
+
+	public Point2D transform(Point2D position) {
+		return new Point2D(position.getX(), height - position.getY());
+	}
+}
\ No newline at end of file