1.

On to a sphere of radius R//2 and density P_(2) with centre at C_(2) a second solid sphere is moulded with density p_(1) radius R and centre C_(1). Find the force experienced by a point mass m at point P at a distance y from the combination as shown.

Answer»

Solution :If we consider that a sphere of RADIUS `R` is PLACED with centre at `C_(1)` od density `rho_(1)` the force on the mass at `P` is
`F_(1)=G((4//3)piR^(3)rho_(1)m)/((R+y)^(2))` towards the sphere.
If we consider that a sphere of radius `R//2` is placed with centre at `C_(2)` of density `rho_(1)` the force on the mass at `P` is
`F_(2)=G((4//3)pi(R//2)^(3)rho_(1)m)/((R//2+R+y)^(2))` towards the sphere.
If we consider that a sphere of radius `R//2` is placed with centre at `C_(2)` of density `rho_(2)` the force on the mass in at `P`
`F_(3)=(G(4//3)pi(R//2)^(3)rho_(2)m)/((R//2+R+y)^(2))`
By the PRINCIPLE of superposition
`F=F_(1)-F_(2)+F_(3)=(4)/(3)piR^(3)Gm[(rho_(1))/((R+y)^(2))+((rho_(2)-rho_(1))//8)/(((3R//2)+y)^(2))]`


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