Question

1.A ring is cut from a platin tube with 8.5cm internal and 8.7cm external diameters.It is supported horizontally from the pan of a balance so that if comes in contact with water in a glass vessel.If an extra 3.97gmwt is required to pull it out of water will be

Answer 1

There is surface tension in play here on the surface of water.  That pulls the ring downwards when water comes in contact with the surface of ring.  We assume that only the bottom surface is in contact.

The length of linear contact between water and the ring
    = L = 2 π R1 + 2 π R2 = 2 π 17.2/100 m = 0.344 π  meters

Surface tension of water at room temperature = S = 0.075 N/m

Total force by which water pulls the ring down = L * S
     = 0.0258 π  Newtons.