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A spring mass system is hanging from the ceiling of a lift. It has been like this for quite some time. Suddenly the cables holding the lift are cut. What will be the amplitude of oscillation of the block when observed by a person standing (of mass M) in the lift?(a) mg/k(b) (M-m)g/k(c) The observer will not observe a SHM(d) 2mg/kThis question was posed to me in an online interview.I'd like to ask this question from Oscillations in chapter Oscillations of Physics – Class 11

Answer» CORRECT OPTION is (a) mg/k

To elaborate: When the system was stationary, the extension in the spring will be xo such that kxo= mg or x0 = mg/k.

When the cables are cut, the entire system will be in free fall.The observer will add a pseudo force on the block upwards and EQUAL to mg.

Now the spring has an extension of mg/kand the restoring force by the spring will be CORRESPONDING to this extension,so the AMPLITUDE of SHM for the observer is mg/k.


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