Question

straight rod of negligible mass is mounted on a frictionless pivot and masses $2.5 \,kg$ and $1\, kg$ are suspended at distances $40 \,cm$ and $100 \,cm$ 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
$2.5\, g \cdot 4 \,\cos \,\theta- 1\,g .100\, \cos\, \theta=0$
So rod remains stationary after the release.