<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html><head> <meta content="text/html; charset=UTF-16" http-equiv="content-type"><title>Ondes progressives, niveau sonore, diffraction, Doppler, concours Puissance 11 ( Fesic ) 2013</title></head><body style="background-color: rgb(255, 255, 255);" alink="#0099ff" vlink="#0099ff"> <small>&nbsp; <big>Aurélie 22/05/13</big> </small> <center><small>&nbsp; </small> <p> <table border="0"> <tbody> <tr> <td width="1373"><small> </small> <center><small>&nbsp; </small> <p><small><font color="#000000" face="Times New Roman" size="+2"><small><big><span style="font-weight: bold;">Ondes progressives, niveau sonore, diffraction, Doppler, concours Puissance 11 ( Fesic ) 2013</span></big><small>.</small></small></font></small></p> <p><font color="#009900"><font color="#009900"><font color="#009900"><font color="#009900"><font color="#009900"><small style="color: black;"><small><em style="font-family: Georgia,&quot;Times New Roman&quot;,Times,serif; 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/* large */ google_ad_slot = "5122043886"; google_ad_width = 300; google_ad_height = 600; //--> </script> <script type="text/javascript" src="http://pagead2.googlesyndication.com/pagead/show_ads.js"> </script></p> <p> <script language="" type="text/javascript"><!-- google_ad_client = "pub-0015053057299262"; google_ad_width = 120 ; google_ad_height = 90; google_ad_format = "120x90_0ads_al_s"; google_ad_channel = ""; google_color_border = "2BA94F"; google_color_bg = "FFFFFF"; google_color_link = "CC0000"; google_color_text = "000000"; google_color_url = "CC0000"; //--></script> <script language="" type="text/javascript" src="http://pagead2.googlesyndication.com/pagead/show_ads.js"></script></p> </center> <br> </td> <td style="text-align: center; color: rgb(0, 153, 0); font-weight: bold;" height="22"><span style="font-weight: normal; color: black;"><span style="font-weight: bold; text-decoration: underline;"></span><span style="font-family: Times New Roman,Times,serif;"><span style="font-weight: bold; text-decoration: underline;"></span><span style="font-weight: bold; text-decoration: underline;"></span><span style="font-weight: bold; color: black; text-decoration: underline;"></span><span style="text-decoration: underline;"></span><span style="font-weight: bold; text-decoration: underline;"></span><span style="font-weight: bold; color: rgb(0, 153, 0);"></span><span style="font-weight: bold; text-decoration: underline;"></span></span></span><span style="font-weight: normal; color: black;"></span><span style="font-weight: normal; color: black;"><span style="font-family: Times New Roman,Times,serif;"><span style="color: black;"><span style="text-decoration: underline; font-weight: bold;"></span><span style="font-weight: bold; font-style: italic;"></span><span style="font-weight: bold;"><span style="text-decoration: underline;"></span><span style="color: rgb(0, 153, 0);"></span></span><span style="text-decoration: underline; font-weight: bold;">Ondes progressives sinusoïdales</span>.<br> Une onde périodique circulaire de fréquence f = 30 Hz est produite à la surface d'un liquide par une pointe qui vibre de manière sinusoïdale. Les cercles représentent les crêtes, c'est-à-dire les maxima de vibration à une date donnée.<br> <img style="width: 225px; height: 223px;" alt="" src="image/fesic16.jpg"><br> a) L'onde est transversale. Vrai.<br> b) La longueur d'onde <span style="font-family: Symbol;">l</span> est de 15 cm. Faux.<br> <span style="font-style: italic;">45 cm correspondent à la distance entre 9 crêtes successives soit 9 longueurs d'onde : </span><span style="font-family: Symbol; font-style: italic;">l</span><span style="font-style: italic;"> = 5 cm</span>. <br> c) La célérité de l'onde est V = 1,5 m/s. Vrai.<br> <span style="font-style: italic;">V = </span><span style="font-family: Symbol; font-style: italic;">l</span><span style="font-style: italic;"> f = 0,05*30 = 1,5 m /s</span>.<br> d) L'onde passant par A arrive en B avec un retard <span style="font-family: Symbol;">t</span> = 100 ms. Vrai.<br> <span style="font-style: italic;">A et B sont distants de 3 longueurs d'onde ce qui correspond à trois périodes temporelles : 3/30 = 0,10 s = 100 ms</span>.<br> <span style="font-weight: bold; color: black; text-decoration: underline;">Concert</span> :<br> </span></span></span><font color="#009900"><span style="font-weight: normal; color: black;"><span style="font-family: Times New Roman,Times,serif;"><span style="color: black;">Un groupe de rock amateur comprend une guitare basse, une guitare, un clavier, une batterie et un chanteur. À dix mètres de la scène, le niveau sonore L, exprimé en décibel (dB), est de :<br> 60 dB pour le chanteur seul ; 57 dB pour la guitare basse seule ; 60 dB pour la guitare seule ; 60dB pour la batterie seule ; 63 dB pour le clavier seul.<br> <span style="text-decoration: underline;">Données</span> : Intensité sonore de référence I<sub>0</sub>= 1,0 x 10<sup>-12</sup>W.m<sup>-2</sup>;<br> log (A x B) = log A + log B; 10 x log 2 = 3.<br> a) Lors du solo de guitare, l'intensité sonore est de I = 1,0 x 10<sup>-6</sup> Wm<sup>-2</sup>. Vrai.<br> <span style="font-style: italic;">I = 10</span><sup style="font-style: italic;">-12</sup><span style="font-style: italic;"> 10</span><sup style="font-style: italic;">6</sup><span style="font-style: italic;"> = </span></span></span></span></font><font color="#009900"><font color="#009900"><span style="font-weight: normal; color: black;"><span style="font-family: Times New Roman,Times,serif;"><span style="color: black;"><span style="font-style: italic;">1,0 x 10</span><sup style="font-style: italic;">-6</sup><span style="font-style: italic;"> Wm</span><sup style="font-style: italic;">-2</sup>.</span></span></span></font></font><br> <font color="#009900"><span style="font-weight: normal; color: black;"><span style="font-family: Times New Roman,Times,serif;"><span style="color: black;">b) Le niveau sonore du groupe lorsqu'ils jouent tous ensemble est de 300 dB. Faux.<br> <span style="font-style: italic;">Intensité sonore totale : 10</span><sup style="font-style: italic;">-12</sup><span style="font-style: italic;"> ( 10</span><sup style="font-style: italic;">6</sup><span style="font-style: italic;"> + 10</span><sup style="font-style: italic;">5,7</sup><span style="font-style: italic;">+10</span><sup style="font-style: italic;">6</sup><span style="font-style: italic;"> +10</span><sup style="font-style: italic;">6</sup><span style="font-style: italic;"> + 10</span><sup style="font-style: italic;">6,3</sup><span style="font-style: italic;">) =10</span><sup style="font-style: italic;">-6</sup><span style="font-style: italic;">(1+0,5+1+1+2) =5,5 10</span><sup style="font-style: italic;">-6</sup><span style="font-style: italic;"> W m</span><sup style="font-style: italic;">-2</sup><span style="font-style: italic;">.</span><br style="font-style: italic;"> <span style="font-style: italic;">Niveau sonore total : L = 10 log(5,5 10</span><sup style="font-style: italic;">-6</sup><span style="font-style: italic;"> / 10</span><sup style="font-style: italic;">-12</sup><span style="font-style: italic;">) =67,4 dB</span>.<br> Lorsque le chanteur et la guitare sont les seuls en action :<br> c) L'intensité sonore est de 1,0 x 10<sup>-3</sup> W m<sup>-2</sup>. Faux.<br> <span style="font-style: italic;">I =10</span><sup style="font-style: italic;">-12</sup><span style="font-style: italic;">(10</span><sup style="font-style: italic;">6</sup><span style="font-style: italic;">+10</span><sup style="font-style: italic;">6</sup><span style="font-style: italic;">) = 2 10</span><sup style="font-style: italic;">-6</sup><span style="font-style: italic;"> W m</span><sup style="font-style: italic;">-2</sup>.<br> d) Le niveau sonore est de 63 dB. Vrai.<br> <span style="font-style: italic;">L = 10 log(2 10</span><sup style="font-style: italic;">-6</sup><span style="font-style: italic;">/10</span><sup style="font-style: italic;">-12</sup><span style="font-style: italic;">) =63 dB</span>.<br> <span style="font-weight: bold; color: rgb(0, 153, 0);"></span></span></span></span></font><font color="#009900"><font color="#009900"><font color="#009900"><font color="#009900"><span style="color: black; font-weight: normal;"><span style="font-family: Times New Roman,Times,serif;"></span></span></font></font></font></font><font color="#009900"><font color="#009900"><font color="#009900"><font color="#009900"><font color="#009900"><span style="color: black; font-weight: normal;"><span style="font-family: Times New Roman,Times,serif;"><br> </span></span></font></font></font></font></font><font color="#009900"><span style="font-weight: normal; color: black;"><span style="font-family: Times New Roman,Times,serif;"><span style="color: black;"></span></span></span></font> <span style="font-weight: normal; color: black;"></span><font color="#009900"><font color="#009900"><span style="font-weight: normal; color: black;"></span></font></font><font color="#009900"><font color="#009900"><font color="#009900"><font color="#009900"><font color="#009900"><span style="font-weight: normal; color: black;"><span style="font-family: Times New Roman,Times,serif;"><span style="color: black;"></span></span></span></font></font></font></font></font><font color="#009900"><font color="#009900"><font color="#009900"><span style="font-weight: normal; color: black;"><span style="font-family: Times New Roman,Times,serif;"><span style="color: black;"></span></span></span></font></font></font><span style="font-weight: normal; color: black;"></span><font color="#009900"><font color="#009900"><font color="#009900"><font color="#009900"><font color="#009900"><font color="#009900"><font color="#009900"><font color="#009900"><font color="#009900"><font color="#009900"><font color="#009900"><font color="#009900"><font face="Times New Roman"><span style="font-weight: normal; 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color: black;"></span></font></font></font></font></font></font><font color="#009900"><font color="#009900"><font color="#009900"><span style="font-weight: normal; color: black;"></span></font></font></font><font color="#009900"><span style="font-weight: normal; color: black;"></span></font><font color="#009900"><font color="#009900"><span style="font-weight: normal; color: black;"></span></font></font></td> </tr> </tbody> </table> <span style="color: black;"><span style="font-family: Times New Roman,Times,serif;"><span style="font-weight: bold; color: rgb(0, 153, 0);"></span></span></span></font><span style="font-family: Times New Roman,Times,serif;"><span style="text-decoration: underline; font-weight: bold;"></span></span><span style="font-family: Times New Roman,Times,serif;"><span style="font-weight: bold; color: rgb(0, 153, 0);"></span></span><font color="#009900"><span style="color: black;"><span style="font-family: Times New Roman,Times,serif;"></span></span></font></small></p> <small><span style="font-weight: bold; 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text-decoration: underline;"></span> </small> <table style="text-align: left; width: 1279px; margin-left: auto; margin-right: auto; height: 32px;" border="0" cellpadding="2" cellspacing="2"> <tbody> <tr> <td style="vertical-align: top; text-align: center;" width="249"><small><br> <script language="" type="text/javascript"><!-- google_ad_client = "pub-0015053057299262"; google_ad_width = 336; google_ad_height = 280; google_ad_format = "336x280_as"; google_ad_type = "text_image"; google_ad_channel = ""; google_color_border = "FFFFFF"; google_color_bg = "FFFFFF"; google_color_link = "CC0000"; google_color_text = "000000"; google_color_url = "11593C"; //--></script> <script language="" type="text/javascript" src="http://pagead2.googlesyndication.com/pagead/show_ads.js"></script></small></td> <td style="vertical-align: top; text-align: center;" width="1016"><small><font color="#009900"><font color="#009900"><font color="#009900"><font color="#009900"><font style="font-weight: normal;" color="#009900"><font style="color: black;" color="#009900"><big><span style="font-family: Times New Roman,Times,serif; color: black; font-weight: bold; text-decoration: underline;"></span><span style="font-family: Times New Roman,Times,serif; color: black;"></span></big></font></font></font></font></font></font></small><small><font color="#009900"><font color="#009900"><font color="#009900"><font color="#009900"><font style="font-weight: normal;" color="#009900"><font style="color: black;" color="#009900"><big><span style="font-family: Times New Roman,Times,serif;"></span></big></font></font></font></font></font></font></small><small><font color="#009900"><font color="#009900"><font color="#009900"><font color="#009900"><font style="font-weight: normal;" color="#009900"><font style="color: black;" color="#009900"><big><span style="font-family: Times New Roman,Times,serif; color: black;"></span></big></font></font></font></font></font></font></small><small><font color="#009900"><font color="#009900"><font color="#009900"><font color="#009900"><font style="font-weight: normal;" color="#009900"><font style="color: black;" color="#009900"><big><span style="font-family: Times New Roman,Times,serif;"><span style="font-weight: bold; color: rgb(0, 153, 0);"></span></span></big></font></font></font></font></font></font></small><font color="#009900"><small><big><font color="#009900"><span style="font-weight: normal; color: black;"><span style="font-family: Times New Roman,Times,serif;"><span style="color: black;"><span style="font-weight: bold; text-decoration: underline;"></span></span></span></span></font></big></small></font><font color="#009900"><small><big><font color="#009900"><span style="font-weight: normal; color: black;"><span style="font-family: Times New Roman,Times,serif;"><span style="color: black;"></span></span></span></font></big></small></font><font color="#009900"><small><big><font color="#009900"><span style="font-weight: normal; color: black;"><span style="font-family: Times New Roman,Times,serif;"><span style="color: black;"><span style="font-weight: bold; text-decoration: underline;"></span><span style="font-weight: bold; color: rgb(0, 153, 0);"></span></span></span></span></font></big></small></font><font color="#009900"><small><big><font color="#009900"><span style="font-weight: normal; color: black;"><span style="font-family: Times New Roman,Times,serif;"><span style="color: black;"><span style="font-weight: bold;"><span style="text-decoration: underline;"></span></span></span></span></span></font></big></small></font><font color="#009900"><small><big><font color="#009900"><span style="font-weight: normal; color: black;"><span style="font-family: Times New Roman,Times,serif;"><span style="color: black;"></span></span></span></font></big></small></font><font color="#009900"><small><big><font color="#009900"><span style="font-weight: normal; color: black;"><span style="font-family: Times New Roman,Times,serif;"><span style="color: black;"></span></span></span></font></big></small></font><font color="#009900"><small><big><font color="#009900"><span style="font-weight: normal; color: black;"><span style="font-family: Times New Roman,Times,serif;"><span style="color: black;"></span></span></span></font></big></small></font><small><font color="#009900"><font color="#009900"><font color="#009900"><font color="#009900"><font style="font-weight: normal;" color="#009900"><font style="color: black;" color="#009900"><big><span style="font-family: Times New Roman,Times,serif;"></span></big></font></font></font></font></font></font></small><small><font color="#009900"><font color="#009900"><font color="#009900"><font color="#009900"><font style="font-weight: normal;" color="#009900"><font style="color: black;" color="#009900"><big><span style="font-family: Times New Roman,Times,serif;"><span style="font-family: Symbol;"><span style="font-family: Times New Roman;"></span></span></span></big></font></font></font></font></font></font></small><small><font color="#009900"><font color="#009900"><font color="#009900"><font color="#009900"><font style="font-weight: normal;" color="#009900"><font style="color: black;" color="#009900"><big><span style="font-family: Times New Roman,Times,serif;"></span></big></font></font></font></font></font></font></small><small><big><span style="font-weight: bold; color: rgb(0, 153, 0);"></span><span style="text-decoration: underline; font-weight: bold;">Diffraction par une fente</span>.<br> On éclaire une fente de largeur a = 0,063 mm à l'aide d'un laser émettant un faisceau rouge de longueur d'onde dans le vide <span style="font-family: Symbol;">l</span> = 633 nm.<br> Un écran est situé à une distance D = 2,0 m de la fente.</big></small><br> <font color="#009900"><span style="font-weight: normal; color: black;"><span style="font-family: Times New Roman,Times,serif;"><span style="color: black;"></span></span></span></font><img style="width: 598px; height: 233px;" alt="" src="image/fesic17.jpg"><br style="font-weight: bold; color: rgb(0, 153, 0);"> <span style="font-weight: bold; text-decoration: underline; color: rgb(0, 153, 0);"></span><span style="color: black;">a) L'écart angulaire <span style="font-family: Symbol;">q</span> de l'onde diffractée est d'environ 0,010°. Faux.<br> <span style="font-family: Symbol; font-style: italic;">q</span><span style="font-style: italic;"> =</span><span style="font-family: Symbol; font-style: italic;"> l</span><span style="font-style: italic;"> / a = 633 10</span><sup style="font-style: italic;">-9</sup><span style="font-style: italic;"> / (0,063 10</span><sup style="font-style: italic;">-3</sup><span style="font-style: italic;">) = 1,0 10</span><sup style="font-style: italic;">-2</sup><span style="font-style: italic;"> rad</span>.<br> b) La largeur de la tache centrale de diffraction sur l'écran a une taille de 4,0 cm. Vrai<br> <span style="font-family: Symbol; font-style: italic;">q</span><span style="font-style: italic;"> ~½L / D ; L = 2</span><span style="font-family: Sylfaen; font-style: italic;">q</span><span style="font-style: italic;">D = 2 10</span><sup style="font-style: italic;">-2</sup><span style="font-style: italic;"> *2 = 0,04 m= 4,0 cm</span>.<br> c) L'écart angulaire aurait été plus grand si le faisceau laser utilisé pour l'expérience avait été vert. Faux.<br> <span style="font-style: italic;">La longueur d'onde du vert ( dans le vide ) est inférieure à celle du rouge ; l'écart angulaire est proportionnel à la longueur d'onde</span>.<br> d) Si on multiplie par deux la distance entre le laser et la fente, la largeur de la tache centrale de diffraction augmente. Faux.</span><br> <span style="font-weight: bold; color: rgb(0, 153, 0);"></span>.<br> </td> </tr> </tbody> </table> <small><span style="font-weight: bold; text-decoration: underline;"></span><br> <span style="font-weight: bold; color: rgb(0, 153, 0);"></span><font color="#009900"><font color="#009900"><font color="#009900"><span style="font-weight: normal; color: black;"><span style="font-family: Times New Roman;"></span></span></font></font></font><span style="color: black;"></span><span style="font-weight: normal; color: black;"></span> <font color="#000000"><b><i><br> </i></b> <table border="0"> <tbody> <tr> <td> <center> <script language="" type="text/javascript"><!-- google_ad_client = "pub-0015053057299262"; google_ad_width = 728; google_ad_height = 15; google_ad_format = "728x15_0ads_al"; google_ad_channel = ""; google_color_border = "2BA94F"; google_color_bg = "FFFFFF"; google_color_link = "CC0000"; google_color_text = "000000"; google_color_url = "CC0000"; //--></script> <script language="" type="text/javascript" src="http://pagead2.googlesyndication.com/pagead/show_ads.js"></script></center> <br> </td> </tr> </tbody> </table> </font> <font color="#000000"> </font> </small> <p> <table style="margin-right: auto; 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font-weight: normal;"></span><span style="font-weight: normal;"></span><span style="font-weight: normal;"></span><span style="font-weight: normal;"> </span><span style="color: rgb(0, 153, 0);"></span><span style="font-weight: normal;"></span><span style="font-weight: normal;"></span><span style="font-weight: normal;"></span><span style="font-weight: normal;"></span> <span style="font-weight: normal;"><span style="color: rgb(0, 153, 0);"><span style="color: black;"></span></span></span><span style="font-weight: normal;"></span><span style="font-weight: normal;"></span><span style="font-weight: normal;"></span><span style="font-weight: normal;"></span><span style="font-weight: normal;"></span><span style="font-weight: normal;"></span><span style="font-weight: normal;"></span><span style="font-weight: normal;"></span><font style="font-weight: normal;" color="#009900"><span style="font-family: Times New Roman,Times,serif;"><span style="color: black;"><span style="font-weight: normal;"></span></span></span></font><span style="font-weight: normal;"><span style="font-weight: bold; text-decoration: underline;"></span></span><span style="font-weight: bold; color: rgb(0, 153, 0);"></span><span style="color: rgb(0, 153, 0); font-weight: bold;"></span><span style="font-weight: bold; color: rgb(0, 153, 0);"></span><span style="font-weight: normal;"></span><span style="font-weight: normal;"></span><span style="font-weight: normal;"></span><span style="font-weight: normal;"></span><span style="font-weight: normal;"></span> <span style="font-weight: normal;"></span><font color="#009900"><span style="font-weight: normal; color: black;"><span style="font-family: Times New Roman,Times,serif;"><span style="font-weight: bold; color: rgb(0, 153, 0);"></span></span></span></font></small> <p style="font-weight: normal;"><small><big><font color="#009900"><font color="#009900"><font color="#009900"><span style="font-weight: normal; color: black;"><span style="font-family: Times New Roman,Times,serif;"><span style="color: black;"><span style="color: black;"><span style="font-weight: bold; text-decoration: underline;"></span><span style="font-weight: bold; color: rgb(0, 153, 0);"><span style="color: black;"></span></span><span style="color: rgb(0, 153, 0);"><span style="color: black;"><span style="font-weight: bold; text-decoration: underline;"></span></span></span><span style="color: black;"><span style="font-weight: bold; text-decoration: underline;">Effet Doppler</span>.<br> En un point 0, un véhicule muni d'une sirène émet un son de fréquence f= 1020 Hz. Le son émis se propage dans l'air à la vitesse de V<sub>son</sub>= 340 m.s<sup>-1</sup>. <br> Un observateur immobile est situé au point M à une distance d = 680 m.<br> Données :1020/340 = 3 ; 340 / 1020 = 0,33 ; 1122 / 1020 = 1,10 ; 918 / 1020 = 0,90.<br> La fréquence f<sub>R</sub> du signal reçu dépend de la vitesse V<sub>E</sub> et de la fréquence f<sub>E</sub> de l'émetteur selon la relation : f<sub>R</sub> =f<sub>E</sub> x(l ± V<sub>E </sub>/V<sub>son</sub>).<br> Le choix du signe + ou - dans la relation dépend du rapprochement ou de l'éloignement de l'émetteur par rapport au récepteur.<br> <span style="text-decoration: underline;">Première phase</span> : Le véhicule est immobile<br> a) La longueur d'onde du son émis est <span style="font-family: Symbol;">l</span> = 3,0 m. Faux.<br> <span style="font-family: Symbol; font-style: italic;">l</span><span style="font-style: italic;"> = V</span><sub style="font-style: italic;">son</sub><span style="font-style: italic;"> / f = 340 / 1020 = 0,33 m</span>.<br> b) L'observateur perçoit le son avec un retard <span style="font-family: Symbol;">t</span> = 2,0 s. Vrai.<br> <span style="font-style: italic;">680 / 340 = 2,0 s</span>.<br> <span style="text-decoration: underline;">Seconde phase</span> : Le véhicule se déplace à vitesse constante vers l'observateur selon une droite de direction OM.<br> c) Le son perçu par l'observateur est plus aigu. Vrai.<br> <span style="font-style: italic;">f</span><sub style="font-style: italic;">R</sub><span style="font-style: italic;"> =f</span><sub style="font-style: italic;">E</sub><span style="font-style: italic;"> x(l + V</span><sub style="font-style: italic;">E </sub><span style="font-style: italic;">/V</span><sub style="font-style: italic;">son</sub><span style="font-style: italic;">) ; f</span><sub style="font-style: italic;">R</sub><span style="font-style: italic;"> &gt; f</span><sub style="font-style: italic;">E</sub><span style="font-style: italic;"> ; si la fréquence augmente le son est plus aigu</span>.<br> </span></span></span></span></span></font></font></font></big></small><small><big><font color="#009900"><font color="#009900"><font color="#009900"><span style="font-weight: normal; color: black;"><span style="font-family: Times New Roman,Times,serif;"><span style="color: black;"><span style="color: black;"><span style="color: black;">d) La vitesse du véhicule est V<sub>E</sub>= 34 m/s pour une fréquence perçue de 1122 Hz. Faux.<br> </span></span></span></span></span></font></font></font></big></small><small><big><font color="#009900"><font color="#009900"><font color="#009900"><span style="font-weight: normal; color: black;"><span style="font-family: Times New Roman,Times,serif;"><span style="color: black;"><span style="color: black;"><span style="color: black;"><span style="font-style: italic;">f</span><sub style="font-style: italic;">R</sub><span style="font-style: italic;"> -f</span><sub style="font-style: italic;">E</sub><span style="font-style: italic;"> =f<sub>E</sub> V</span><sub style="font-style: italic;">E </sub><span style="font-style: italic;">/V</span><sub style="font-style: italic;">son</sub><span style="font-style: italic;"> ; 2 = 1120 *V<sub>E</sub> / 340 ; 2 = 3 V<sub>E</sub> ; V<sub>E</sub> = 2/3 m/s.</span></span></span></span></span></span></font></font></font></big></small><br> </p> <span style="font-weight: normal;"><br> </span> <small><span style="font-weight: normal;"><span style="font-weight: bold; color: rgb(0, 153, 0);"></span></span><span style="font-weight: normal;"></span><span style="font-weight: normal;"><span style="font-weight: bold; color: rgb(0, 153, 0);"></span></span><span style="font-weight: normal;"></span> </small></td> </tr> </tbody> </table> </p> <table border="0"> <tbody> <tr> <td><small> </small> <center><small> <font color="#000000"> <script language="" type="text/javascript"><!-- google_ad_client = "pub-0015053057299262"; google_ad_width = 728; google_ad_height = 15; google_ad_format = "728x15_0ads_al"; google_ad_channel = ""; google_color_border = "2BA94F"; google_color_bg = "FFFFFF"; google_color_link = "CC0000"; google_color_text = "000000"; google_color_url = "CC0000"; //--></script> <script language="" type="text/javascript" src="http://pagead2.googlesyndication.com/pagead/show_ads.js"></script></font></small></center> <small><font color="#000000"><br> </font></small></td> </tr> </tbody> </table> <small><span style="font-weight: bold; text-decoration: underline;"></span><br> </small> <hr noshade="noshade" width="10%"><small><span style="font-weight: bold; text-decoration: underline;"></span><span style="font-family: Times New Roman,Times,serif;"><span style="font-weight: normal;"><span style="text-decoration: underline;"></span></span></span><span style="font-family: Times New Roman,Times,serif;"><span style="font-weight: normal;"></span></span><span style="font-family: Times New Roman,Times,serif;"><span style="font-weight: normal;"></span></span> <span style="font-weight: bold; color: rgb(0, 153, 0);"></span><span style="font-weight: bold; text-decoration: underline;"></span><span style="font-weight: bold; color: rgb(0, 153, 0);"></span><span style="font-weight: bold; text-decoration: underline;"></span><font color="#009900"><font color="#009900"><font color="#009900"><span style="color: black;"></span></font></font></font><font color="#009900"><font color="#009900"><font color="#009900"><font color="#009900"><span style="color: black;"><span style="font-style: italic;"></span></span></font></font></font></font><span style="font-weight: normal;"><span style="font-weight: bold; color: rgb(0, 153, 0);"></span></span><font color="#000000" face="Times New Roman"><span style="font-weight: bold; color: rgb(0, 153, 0);"></span></font><span style="font-weight: normal;"></span><span style="text-decoration: underline; font-weight: bold;"></span><span style="color: rgb(0, 153, 0);"><span style="color: black;"><span style="font-family: Times New Roman,Times,serif; font-weight: normal;">&nbsp;</span></span></span><span style="text-decoration: underline; font-weight: bold;"></span>&nbsp;<span style="font-weight: normal;"><br> </span> </small></center> </td> </tr> <tr> <td style="text-align: center;" width="1373"><small><span style="font-weight: normal;"><span style="text-decoration: underline;"></span></span><span style="font-weight: normal;"></span><span style="font-weight: bold; color: rgb(0, 153, 0);"></span></small><span style="font-family: Times New Roman,Times,serif;"></span><span style="font-family: Times New Roman,Times,serif;"></span><span style="font-family: Times New Roman,Times,serif;"><br> </span><small> <span style="font-weight: bold; text-decoration: underline;"></span><br> </small></td> </tr> <tr> <td width="1373"><small> </small> <center><small><a href="../../index.htm"><font size="+2"><small>menu</small></font></a></small></center> </td> </tr> </tbody> </table> </p> </center> </body></html>