Question

suppose the earth shrinks such that its radius decreases of half the present value what will be the acceleration due to gravity on the surface

Answer 1

since we know g=GM/R²
so if the radius decrease by half then new value of g will be equal to GM/(R/2)²
4GM/R²
which means that the acceleration due to gravity will increase by 4 times

Answer 2

g=GM/(R/2)^2

g=4GM/R^2

g=4g(g=GM/R^2)

g=4×9.8

g=39.2 so it increases 4 times