The radii of two spheres are 2 cm and 4 cm, and they carry 1000 C and 2000 C charges, respectively. What will be the ratio of their surface charge density? a) 4:1
b) 1:2
c)1:4
d)2:1

Panel bc in fig. p2.76 is semi-circular, with the 3 meter radius and horizontal straight edge through point b. compute (a) the hydrostatic force of the water on the panel, (b) its center of pressure, and (c) the moment of this force about point b. assume atmospheric pressure on the dry side of the panel