Question

straight rod of negligible mass is mounted on a frictionless pivot and masses $2.5kg$ and $1kg$ are suspended at distances $40cm$ and $100cm$ respectively from the pivot as shown. The rod is held at an angle $\theta$ with the horizontal and released.

• A. The rod executes periodic motion about horizontal position after the release
• B. The rod remains stationary after the release
• C. The rod comes to rest in vertical position with 2.5 kg mass at the lowest point
• D. The rod executes periodic motion about vertical position after the release

Answer 1

Answer: (B)

Torque about hinge
$2.5g\cdot 4\cos \theta -1g.100\cos \theta =0$
So rod remains stationary after the release.