Two men, each of mass 75 kg, stand on the rim of a horizontal large disc, diametrically opposite to each other. The disc has a mass 450 kg and is free to rotate about its axis. Each man simultaneously start along the rim clockwise with the same speed and reaches their original starting points on the disc. The angle turned by the disc with respect to the ground in this duration is 5 nπ. Find n.
Physics · Rotational Motion · angular momentum in pure rotation and its conservation
JEE Mains

Question

Two men, each of mass 75 kg, stand on the rim of a horizontal large disc, diametrically opposite to each other. The disc has a mass 450 kg and is free to rotate about its axis. Each man simultaneously start along the rim clockwise with the same speed and reaches their original starting points on the disc. The angle turned by the disc with respect to the ground in this duration is 5 nπ. Find n.

Physics · Rotational Motion · angular momentum in pure rotation and its conservation

G1 Physics · Accepted Answer

Write translation ΣF=Ma and rotation Στ about CM=I about CMα, together with the no-slip relation v of CM=ωR and a of CM=αR whenever pure rolling applies. Solving the equations for the shown geometry gives 4.