gravitation

Option b and c are redundant because value of g is maximum at the surface of the Earth..

I feel it should be option d) decreases

that is when h<<R,

g'=g(1 - h/R)

Acc due to grav blow earths surface at depth 'h'= g_b=g ( 1- h/R) and above g_a=g (1-2h/R). Ratio g_b/g_a =(1-h/R) (1-h/2R)^-1. Since h<<R therefore considering only the first term of the expansion we get( 1- h/R) (1+ h/2R).This gives 1- h/R + 2h/R - 2h²/R². Neglecting the higher powers of h/R and simplifying we get 1+ h/R. This quantity will increase linearly with 'h'. So (b) is correct

I feel the answer is option (d) though not sure :P

my mistake..I didnt read the question properly.. Yes.. Agree with sengupta..

tha answer is (b)

Nice Sengupta... Subho What have you decided now/?

while calculating gravitational force b/n extended objects can we consider their mass to be concentrated at their centre of masses.
suppose i'm calculating Fg b/n a point mass and rod

0 --------------------------------------------------
m M, length L

and let distence b/N them be d.

Then, after performing integration Fg comes out to be GMm/d(d+L)
BUT, IF WE WOULD HAVE ASSUMED MASS TO BE COMCENTRATED AT ROD'S CENTRE
Fg should have been GMm/(d+L/2)^2
SO, WHATS XRONG IN THE ASSUMPTION....