Liquid drops are falling slowly one by one from a vertical glass tube. Establish a relation between the weight of a drop w, the surface tension land the radius r of the tube (assume the angle of contact to be zero)
 

• A

  $\mathrm{W}={\mathrm{\pi r}}^2\mathrm{T}$

• B

  $\mathrm{W}=2\mathrm{\pi rT}$

• C

  $\mathrm{w}=2{\mathrm{\pi r}}^2\mathrm{T}$

• D

  $\mathrm{W}=\frac{4}{3}{\mathrm{\pi r}}^3\mathrm{T}$