(a) No, because the gravitational force of attraction on a point masssituated inside a spherical shell is zero.
(b) Yes, an astronaut inside the spaceship can detect the variation ingravity, if the size of the spaceship is large enough.
(c) Tidal effect depends inversely on the cube of the distance, unlikeforce, which depends inversely on the square of the distance. Since thedistance of moon from ocean water is very small as compared to thedistance of sun from the ocean water on earth. Therefore, the tidal effectof moon’s pull is greater than the tidal effect of the sun.