diff --git a/notebooks/exercises/particle_update_position.ipynb b/notebooks/exercises/particle_update_position.ipynb
index b3d829a..971107a 100644
--- a/notebooks/exercises/particle_update_position.ipynb
+++ b/notebooks/exercises/particle_update_position.ipynb
@@ -52,20 +52,25 @@
    ],
    "source": [
     "class Particle:\n",
-    "    def __init__(self, mass, velocity):\n",
+    "    def __init__(self, mass, velocity, position):\n",
     "        self.mass = mass\n",
     "        self.velocity = velocity\n",
+    "        self.position = position\n",
     "\n",
     "    def momentum(self):\n",
     "        return self.mass * self.velocity\n",
     "\n",
+    "    def update_position(self, dt):\n",
+    "        self.position = self.position + self.velocity * dt\n",
+    "        return self.position\n",
+    "\n",
     "particle = Particle(mass=2.1, velocity=0.8)\n",
     "print(particle.momentum())"
    ]
   },
   {
    "cell_type": "code",
-   "execution_count": 3,
+   "execution_count": null,
    "metadata": {},
    "outputs": [
     {
@@ -78,7 +83,8 @@
    ],
    "source": [
     "position = 8.2\n",
-    "new_position = update_position(particle.velocity, position, dt=0.1)\n",
+    "particle = Particle(2.1, 0.8, position)\n",
+    "new_position = particle.update_position(dt=0.1)\n",
     "print(new_position)"
    ]
   },