Q.State and prove Bernoulli's theorem. OR What do you mean by viscosity? Obtain an expression for the terminal velocity of a ball falling in a viscous liquid.
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Start your 14-day free trial to unlock the full solution →Applying the work-energy theorem to a fluid element moving along a streamline in an ideal fluid gives Bernoulli's equation, .
Statement: For the streamline flow of an ideal fluid (incompressible, non-viscous, and flowing steadily/non-turbulently), the sum of pressure energy, kinetic energy, and potential energy per unit volume remains constant at every point along a streamline:
Proof (using the work-energy theorem): Consider an ideal fluid flowing steadily through a tube of varying cross-section, from a point 1 (area , height , velocity , pressure ) to point 2 (area , height , velocity , pressure ). By the equation of continuity, .
Considering a small volume (mass ) of fluid pushed from position 1 to position 2:
- Work done by the pressure force pushing the fluid in at point 1:
- Work done against the pressure force at point 2 (fluid pushing out against the fluid ahead):
- Total work done by pressure forces:
By the work-energy theorem, this net work equals the change in total mechanical energy (kinetic + potential) of the fluid element:
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