Question

8£®¹¤µØÉÏÓõõËþºÍ½ðÊôˮͰ´ÓÉî¾®ÖÐÌáË®£¬ÈôˮͰµÄ²ÄÁÏÃܶÈΪ8g/cm³£¬Ë®Í°ÖÊÁ¿Îª4kg£¬Ë®Í°ÈÝ»ýΪ20L£¬µ±Ê¢ÂúË®µÄÍ°´ÓË®ÖÐÂýÂýÌáÉý£¨Í°Ê¼ÖÕ䶳öË®Ã棩ʱ£¬Ð¡Ã÷¶ÔÉþµÄÀ­Á¦ÎªF=25N£®²»¼ÆÉþ×ÓÖØÁ¿ºÍĦ²Á£¬Ë®µÄÃܶÈÊÇ1.0¡Á10³kg/cm³£®gÈ¡10N/kg£®
£¨1£©¶¯»¬ÂÖÓжàÖØ£¿
£¨2£©Ë®Í°Â¶³öË®ÃæÇ°£¬»¬ÂÖ×éµÄ»úеЧÂÊÓжà´ó£¿
£¨3£©Ë®Í°±»ÌáÀë¾®ÖÐË®Ãæºó£¬ÒÔ0.2m/sµÄËÙ¶ÈÔÈËÙÊúÖ±ÉÏÉý£¬Ð¡Ã÷¶ÔÉþ×Ó×ÔÓɶËÀ­Á¦µÄ¹¦Âʶà´ó£¿

Answer 1

·ÖÎö £¨1£©ÀûÓÃG=mgÇó³öˮͰµÄÖØÁ¦£¬¸ù¾ÝˮͰµÄÖÊÁ¿ºÍÃܶÈÇó³öˮͰµÄÌå»ý£¬ÔÙÀûÓÃF_¸¡=pgV_ÅÅÇó³öˮͰÊܵ½µÄ¸¡Á¦£¬Í°Êܵ½µÄÀ­Á¦F=G-F_¸¡£¬ÔÙÀûÓÃÍ°ºÍ»¬ÂÖÊܵ½µÄÀ­Á¦G=nF¼´¿ÉÇó³ö¶¯»¬ÂÖÓжàÖØ£®
£¨2£©¸ù¾ÝСÃ÷¶ÔÉþµÄÀ­Á¦ÎªF=25N£¬Éþ×ÓÊܵ½Ë®Í°µÄÀ­Á¦F_À­=G-F_¸¡£¬ÀûÓæÇ=$\frac{{W}_{ÓÐ}}{{W}_{×Ü}}$¡Á100%¼´¿ÉÇó³ö»¬ÂÖ×éµÄ»úеЧÂÊ£®
£¨3£©ÏÈÇó³öˮͰװÂúʱˮµÄÖÊÁ¿£¬È»ºó¿ÉµÃË®ºÍˮͰµÄ×ÜÖÊÁ¿£¬ÀûÓÃG_×Ü=m_×ÜgÇó³öË®ºÍˮͰµÄ×ÜÖØÁ¦£¬ÔÙ¸ù¾Ý¶¯»¬ÂÖÉÏÓÐÁ½¹ÉÉþ×ÓÇó³öÈ˵ÄÀ­Á¦£¬ÔÙÀûÓÃP=Fv¼´¿ÉÇó³öСÃ÷¶ÔÉþ×Ó×ÔÓɶËÀ­Á¦µÄ¹¦ÂÊ£®

½â´ð ½â£º£¨1£©Ë®Í°µÄÖØÁ¦ÊÇ£ºG=mg=4kg¡Á10N/kg=40N£¬
ˮͰµÄÌå»ýÊÇ£ºV_Í°=$\frac{m}{¦Ñ}$=$\frac{4kg}{8¡Á1{0}^{3}kg/{m}^{3}}$=5¡Á10^-4m³£®
ˮͰÊܵ½µÄ¸¡Á¦ÊÇF_¸¡=¦Ñ_Ë®gV_ÅÅ=¦Ñ_Ë®gV_Í°=1.0¡Á10³kg/m³¡Á10N/kg¡Á5¡Á10^-4m³=5N£¬
Éþ×ÓÊܵ½Ë®Í°µÄÀ­Á¦£ºF_À­=G-F_¸¡=40N-5N=35N£¬
ÒòΪ²»¼ÆÉþ×ÓÖØÁ¿ºÍĦ²Á£¬ÓÐÁ½¹ÉÉþ×Ó³ÐÖØ£¬¹ÊÓУº
F=$\frac{{F}_{À­}+{G}_{¶¯}}{2}$£¬¼´£º25N=$\frac{35N+{G}_{¶¯}}{2}$£¬
½âµÃ£ºG_¶¯=15N£®
£¨2£©Ë®Í°Â¶³öË®ÃæÇ°£¬»¬ÂÖ×éµÄ»úеЧÂÊ£º
¦Ç=$\frac{{W}_{ÓÐÓÃ}}{{W}_{×Ü}}$¡Á100%=$\frac{{F}_{À­}h}{Fs}$¡Á100%=$\frac{35N¡Áh}{25N¡Á2h}$¡Á100%=70%£®
£¨3£©Ë®Í°×°ÂúʱˮµÄÖÊÁ¿ÊÇ£ºm=¦ÑV=1.0¡Á10³ kg/m³¡Á20¡Á10^-3m³=20kg£¬
Ë®ºÍˮͰµÄ×ÜÖÊÁ¿ÊÇ£ºm_×Ü=20kg+4kg=24kg£¬
Ë®ºÍˮͰµÄ×ÜÖØÁ¦ÊÇ£ºG_×Ü=m_×Üg=24kg¡Á10N/kg=240N£¬
È˵ÄÀ­Á¦ÊÇ£ºF¡ä=$\frac{{G}_{×Ü}+{G}_{¶¯}}{2}$=$\frac{240N+15N}{2}$=127.5N£¬
À­Á¦Òƶ¯µÄËÙ¶ÈÊÇ£ºv=2v_Îï=2¡Á0.2m/s=0.4m/s£¬
À­Á¦µÄ¹¦ÂÊÊÇ£ºP=F¡äv=127.5N¡Á0.4m/s=51W£®
´ð£º£¨1£©¶¯»¬ÂÖÓÐ15N£»
£¨2£©Ë®Í°Â¶³öË®ÃæÇ°£¬»¬ÂÖ×éµÄ»úеЧÂÊΪ70%£»
£¨3£©Ð¡Ã÷¶ÔÉþ×Ó×ÔÓɶËÀ­Á¦µÄ¹¦ÂÊΪ51W£®

µãÆÀ ´ËÌâÉæ¼°µ½µÄ֪ʶµã½Ï¶à£¬ÓÐÒ»¶¨µÄ×ÛºÏÐÔ£¬ÄܰѼòµ¥»úеÕⲿ·ÖµÄ֪ʶµãϵͳÆðÀ´£¬×öµ½Ñ§Ð¶øÖª¹Ê£¬ÔÚ֪ʶµÄÈÚ»á¹áͨÖеõ½¸ü´óµÄÌáÉý£®