Multiple choice

The gap between a moving circular plate and a stationary surface is being continuously reduced, as the circular plate comes down at a uniform speed V towards the stationary bottom surface, as shown in the figure. In the process, the fluid contained between the two plates flows out radially. The fluid is assumed to be incompressible and in viscid.

The radial velocity vr at any radius r, when the gap width is h, is

  1. $vr=\frac{V_r}{2h}$
  2. $v_r=\frac{V_r}{h}$
  3. $v_r=\frac{2Vh}{r}$
  4. $v_r=\frac{Vh}{r}$
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Explanation