1.

A planet of mass m moves around the Sum along an elliptical path with a period of revolution T. During the motion, the planet's maximum and minimum distance from Sum is R and (R)/(3) respectively. If T^(2)=alphaR^(3), then the magnitude of constant alpha will be

Answer»

`(10)/(9).(PI)/(Gm)`
`(20)/(27).(pi^(2))/(Gm)`
`(32)/(27).(pi^(2))/(Gm)`
`(1)/(18).(pi^(2))/(Gm)`

Solution :Given mass of PLANET =m
Maximum and minimum distance of the planet from Sum is R and `(R)/(3)`, respectively.
`:.` Semi-major AXIS of elliptcal path of planet around the Sum,
`a=(R+(R)/(3))/(2)=(2R)/(3)`
`:.` Time period of planet is given by
`T=2pisqrt((a^(3))/(Gm))=2pisqrt((((2R)/(3)))/(Gm))^(3)`
`T=2pisqrt((8R^(3))/(27G m))`
Square on the both sides we get
`T^(2)=4pi^(2).(8R^(3))/(27Gm)`
`T^(2)=(32pi^(2))/(27Gm).R^(3)=alphaR^(2)`
`:.alpha=(32pi^(2))/(27Gm)`
HENCE, the MAGNITUDE of constant `alpha` will be `(32)/(27).(pi^(2))/(Gm)`


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