Question no 9 plz explain with explained integration

Question no 9 plz explain with explained integration due to rrnvity of at • Bunt 1000 km above the moon'* The masa of the moon 4 10 and radius 1B 1740 km (9 Two srnall of 10 kg and 20 kg are kept a dustance I m apart nod relea»ed, that only mutual gravitational forces are acting, find the the parocle• when the separation decreases to 05 A semzorcu)ar wire hag a length L and M. A part.•cie of mass m placed at centre the ctrcle. F md the gravitational attraction on the particle due to the wtr•e. 9. an expression for the gravitational field due to a uniform rod of length L and mass M at a pomt on Its bisector at a distance d from the centre. 10. Two concentric sphencal shells have masses M, , M: and radii Ra (R, R,) . What is the force exerted by this system on a particle of mass m, if it is placed at a distance (R, + Ra)/2 from the centre ? 11. A tunnel ig dug along a diameter of the earth. Find

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Dear Student

Let 
u = mass/length =M/L
dm = dx * u 

dE= Gravitational field due to mass dm at d distance on perpendicular bisector of rod.

From symmetry of the rod around its bisector you can easily see that horizontal components of Gravitational field will cancel out as there will be equal field due to mass dm at distance x from centre on both sides of centre, but in opposite directions. 

However the vertical component due to mass dm on either side of centre will add up to give
dEgy =2 * dEg sinϴ = 2 * G(dm) sinϴ/(d2 + x2) =  G(dm) d/(d+ x2)3/2 


Now to find field due to complete rod  we must  integrate dEgy over complete rod

to do that put limit of x from  0 to L/2 and integrate it 

Egy​ = 2GM/d(L2 + 4d2)1/2

so this is the Expession for gravitational field at a poind d on perpendicular bisector.

Regards





 

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