GATE 2020 ME (ME1) – Question 31
A balanced rigid disc on a rigid rotor has four identical 10 g point masses attached to four points on a 100 mm radius circle as shown. The motor drives it at a uniform 10 rad/s. If one mass detaches, find the resultant unbalance force (N), to two decimals.
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Correct answer: .09 to .11
Explanation
The original vector sum of centrifugal forces is zero. Removing one mass leaves a resultant equal and opposite to its force, with magnitude $mr\omega^2=0.010(0.100)(10)^2=\mathbf{0.10}$ N.