1.

A thin and circular disc of mass m and radius R is rotating in a horizontal plane about an axis passing through its centre and perpendicular to its plane with an angular velocity omega . If another disc of same dimension but mass ml4 is placed gently on the first disc co-axially, then the new angular velocity of the system is

Answer»

`5omega//4`
`2omega//3`
`4omega//5`
`3omega//2`

SOLUTION :`I_(1)omega_(1)=I_(2)omega_(2)`
`1/2mR^(2)OMEGA=[1/2mR^(2)+1/2(m/4)R^(2)]omega_(2)=1/2mR^(2)(1+1/4)omega_(2)`
`1/2mR^(2)omega=1/2mR^(2)xx5/4omega_(2)rArr=5/4omega_(2)thereforeomega_(2)=4/5omega`


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