public void update(float gameTime, Camera camera)
  {
    if (isDead)
    {
      return;
    } 
    this.move(this.velocity);
    this.worldPosition.x = this.position.x + camera.getPosition().x;
    this.worldPosition.y = this.position.y + camera.getPosition().y;
    this.velocity.x *= 0.3f;
    this.velocity.y *= 0.9f;
    sprite.update(gameTime);
  }