Find the radius of the spherical cavity that must be drilled at the centre of a solid copper sphere of radius 5cm so that the sphere just floats in water. Density of copper =8.9×103kg m−3, density of water =1.0×103kg m−3.
(a) 4.4cm
(b) 4.0cm
(c) 4.8cm
(d) 4.2cm