Question

We have three disc which is very thin having radius R1 R2&R3 has been colouring both sides of the disc is Rs-1600,400,6400 then find out the ratio of the radius of the disc
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Answer 1

Answer:

Consider an element of the disc of radius x and thichness dx. Mass of the element is dM=M×2πxdx[π(4R)2-π(3R)2]=2M7R2xdx. Gravitational potential at P due to element