1.

A uniform circular disc of mass 400 g and radius 4.0 cm is rotated about one of its diameter at an anglar speed of 10 rot/s. The kinetic energy of the disc is :

Answer»

`3.2xx10^(-5)J`
`1.6xx10^(-3)J`
`3.2xx10^(-2)J`
`6.4xx10^(-4)J`

Solution :K.E. of rotation `E_("rot")=(1)/(2)Iomega^(2)`
`=(1)/(2)((1)/(4)MR^(2)OMEGA^(2))`
`=(1)/(8)xx400xx(4)^(2)XX(20pi)^(2)`
`=800xx400pi^(2)ergs`.
`=320000pi^(2)xx10^(-7)J`
`=32xx(3.142)^(2)xx10^(-3)`
`=3.2xx10^(-1)J`


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