Q: A hollow sphere has a small hole in it. On lowering the sphere in a tank of water, it is observed that water enters into the hollow sphere at a depth of 40cm below the surface. Surface tension of water is 7 × 10-2 N/m. The diameter of the hole is
(a) 1/28 mm
(b) 1/21 mm
(c) 1/14 mm
(d) 1/7 mm
Ans: (c)