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Problems in Mathematical Analysis.pdf - pwp.net.ipl.pt

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Sec. 12] Apply<strong>in</strong>g Def<strong>in</strong>ite Integrals to Solution of Physical <strong>Problems</strong> 175<br />

Whence<br />

r 9 dr^= nco 2 6/? 4 fc<br />

4. Pressure of a liquid. To compute the force of liquid pressure we use<br />

Pascal's law, which states that the force of pressure of a liquid on an area S<br />

at a de<strong>pt</strong>h of immersion h Is<br />

where y is the specific weight of the liquid.<br />

Example 4. F<strong>in</strong>d the force of pressure experienced by a semicircle of<br />

radius r submerged vertically <strong>in</strong> water so that its diameter is flush with the<br />

water surface (Fig 61).<br />

Solution, We partition the area of the semicircle <strong>in</strong>to elements strips<br />

parallel to the surface of the water. The area of one such element (ignor<strong>in</strong>g<br />

higher-order <strong>in</strong>f<strong>in</strong>itesimals) located at a distance h from the surface is<br />

ds ^ 2xdh = 2 V'* h 2 dli.<br />

The pressure experienced by this element is<br />

where y is the specific weight of the water equal to unity.<br />

Whence the entire pressure is<br />

r<br />

= 2 C<br />

J<br />

1751. The velocity of a body thrown vertically upwards with<br />

<strong>in</strong>itial velocity V Q (air resistance neglected), is given by the

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