A uniform rod of mass M and length R/4 is laid radially on a smooth disk rotating at angular speed ω. Its centre is distance R from disk centre. Rod kinetic energy is A Mω²R²/5. Find A. [See Image.]
Physics · Mixed Chapter
JEE Main Practice

Question

A uniform rod of mass M and length R/4 is laid radially on a smooth disk rotating at angular speed ω. Its centre is distance R from disk centre. Rod kinetic energy is A Mω²R²/5. Find A. [See Image.]

Physics · Mixed Chapter

G1 Physics · Accepted Answer

Step 1 — A smooth rotating disk exerts no tangential contact force on a rod just gently placed on it. Step 2 — Therefore the rod cannot be spun up to the disk angular velocity without friction. Step 3 — Initially the rod is at rest relative to laboratory; it remains at rest under only normal and gravitational forces. Step 4 — Rod kinetic energy = 0, so A = 0.