diff --git a/content/videos/challenges/184-elastic-collisions/index.json b/content/videos/challenges/184-elastic-collisions/index.json
index 08e59035a..d9125e3d8 100644
--- a/content/videos/challenges/184-elastic-collisions/index.json
+++ b/content/videos/challenges/184-elastic-collisions/index.json
@@ -76,8 +76,8 @@
         {
           "icon": "📃",
           "title": "Elastic Collisions Formula Derivation",
-          "url": "https://dipamsen.github.io/notebook/collisions.pdf",
-          "description": "Explanation and derivation for formula of elastic collisions, by Dipam Sen."
+          "url": "https://dipamsen.github.io/notebook/page/collisions.pdf",
+          "description": "Explanation and derivation for formula of elastic collisions."
         }
       ]
     }