MOI of Combined Bodies Trick 🔥 | Parallel Axis
❓ Concept Question How do we calculate the moment of inertia of a system of different bodies about a given axis? 🖼 Concept Image ✍️ Short Concept MOI depends on: 👉 Mass distribution 👉 Shape of body 👉 Axis of rotation For multiple bodies → calculate individually and then add. 🔷 Step 1 — MOI Depends on Axis 💯 Moment of inertia is not fixed . It depends on: Shape Mass distribution Axis of rotation 👉 Axis change ⇒ MOI change This is the most important idea. 🔷 Step 2 — Different Bodies, Different MOI Even if mass and radius same , formulas differ: Disc → 1 4 M R 2 \frac{1}{4}MR^2 (about diameter) Solid sphere → 2 5 M R 2 \frac{2}{5}MR^2 Spherical shell → 2 3 M R 2 \frac{2}{3}MR^2 📌 JEE mixes these to create confusion. 🔷 Step 3 — Reference MOI Trick Often given: I = MOI of disc about its diameter I = \text{MOI of disc about its diameter} 👉 Convert all other MOIs into multiples of I This simplifies calculati...