An $$80$$ kg man stands at the edge of a horizontal circular platform having a moment of inertia of $$720$$ $$kgm-2$$ and a radius of $$2$$ m. The platform is initially at rest and is free to rotate about a frictionless, vertical axel through its centre. The man then starts walking around the edge clockwise (as$$ viewed from $$above) at a speed of $$1.5$$ $$m/s$$ relative to the earth then the work done by the man is

Question

An $$80$$ kg man stands at the edge of a horizontal circular platform having a moment of inertia of $$720$$ $$kgm-2$$ and a radius of $$2$$ m.  The platform is initially at rest and is free to rotate about a frictionless, vertical axel through its centre.  The man then starts walking around the edge clockwise (as$$ viewed from $$above) at a speed of $$1.5$$ $$m/s$$ relative to the earth then the work done by the man is

Infinity Learn · Accepted Answer

from conservation of angular momentum mvr $$+$$ Iω $$=o$$ω for the platform $$=mvrI=80$$×$$1.5$$×$$2720=13work$$ done by the man is  $$12mv2+12I$$ω$$21280$$×$$94+72019=130$$

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