Question

7£®ÈçͼËùʾ£¬Ä³´Î»¬Ñ©ÑµÁ·£¬Ô˶¯Ô±Õ¾ÔÚˮƽѩµÀÉϵÚÒ»´ÎÀûÓû¬Ñ©ÕȶÔÑ©ÃæµÄ×÷ÓûñµÃˮƽÍÆÁ¦F=84N¶ø´Ó¾²Ö¹ÏòÇ°»¬ÐУ¬Æä×÷ÓÃʱ¼äΪt₁=1.0 s£®³·³ýˮƽÍÆÁ¦Fºó¾­¹ýt₂=2.0 s£®ËûµÚ¶þ´ÎÀûÓû¬Ñ©ÕȶÔÑ©ÃæµÄ×÷ÓûñµÃͬÑùµÄˮƽÍÆÁ¦£¬×÷ÓþàÀëÓëµÚÒ»´ÎÏàͬ£®ÒÑÖª¸ÃÔ˶¯Ô±Á¬Í¬×°±¸µÄ×ÜÖÊÁ¿Îªm=60kg£¬ÔÚÕû¸öÔ˶¯¹ý³ÌÖÐÊܵ½µÄ»¬¶¯Ä¦²ÁÁ¦´óСºãΪF_f=12N£¬Çó£º
£¨1£©µÚÒ»´ÎÀûÓû¬Ñ©ÕȶÔÑ©Ãæ×÷ÓûñµÃµÄËٶȴóС¼°Õâ¶Îʱ¼äÄÚµÄλÒÆ£»
£¨2£©¸ÃÔ˶¯Ô±£¨¿ÉÊÓΪÖʵ㣩µÚ¶þ´Î³·³ýˮƽÍÆÁ¦ºó»¬ÐеÄ×î´ó¾àÀ룮

Answer 1

·ÖÎö £¨1£©¸ù¾ÝÅ£¶ÙµÚ¶þ¶¨ÂÉÇó³öÀûÓÃÑ©ÕÌ×÷ÓÃʱµÄ¼ÓËٶȣ¬¸ù¾ÝËÙ¶Èʱ¼ä¹«Ê½Çó³öµÚÒ»´ÎÀûÓû¬Ñ©ÕȶÔÑ©Ãæ×÷ÓûñµÃµÄËٶȴóС£¬¸ù¾ÝλÒÆÓëʱ¼ä¹ØϵÇó³öÕâ¶Îʱ¼äÄÚµÄλÒÆ£®
£¨2£©¸ù¾ÝÅ£¶ÙµÚ¶þ¶¨ÂÉÇó³ö³·È¥ÍÆÁ¦ºóµÄ¼ÓËٶȣ¬½áºÏËÙ¶Èʱ¼ä¹«Ê½Çó³ö2sºóµÄËٶȣ¬¸ù¾ÝËÙ¶ÈλÒƹ«Ê½Çó³öÑ©Õ̵Ú2´Î¶ÔÑ©Ãæ×÷ÓúóµÄËٶȣ¬ÔÙ½áºÏËÙ¶ÈλÒƹ«Ê½Çó³öµÚ¶þ´Î³·³ýˮƽÍÆÁ¦ºó»¬ÐеÄ×î´ó¾àÀ룮

½â´ð ½â£º£¨1£©Ô˶¯Ô±Õ¾ÔÚÑ©µÀÉϵÚÒ»´ÎÀûÓû¬Ñ©ÕȶÔÑ©Ãæ×÷ÓÃʱ
¼ÓËÙ¶ÈΪ£º${a}_{1}=\frac{F-f}{m}=\frac{84-12}{60}m/{s}^{2}=1.2m/s$²
t₁=1sʱµÄËÙ¶ÈΪ£º
v₁=a₁t₁=1.2¡Á1m/s=1.2m/s
Õâ¶Îʱ¼äÄÚµÄλÒÆ£º${x}_{1}=\frac{1}{2}{a}_{1}{t}_{1}^{2}=\frac{1}{2}¡Á1.2¡Á{1}^{2}m=0.6m$
£¨2£©µÚÒ»´Î³·³ýˮƽÍÆÁ¦Fºó£¬¼ÓËÙ¶ÈΪ
${a}_{2}=-\frac{f}{m}=-\frac{12}{60}m/{s}^{2}=-0.2m/{s}^{2}$
³·³ýˮƽÍÆÁ¦Fºó¾­¹ýt₂=2.0sËÙ¶ÈΪ£º
v₂=v₁+a₂t₂=1.2-0.2¡Á2m/s=0.8m/s
µÚ¶þ´ÎÀûÓû¬Ñ©ÕȶÔÑ©ÃæµÄ×÷ÓûñµÃͬÑùµÄˮƽÍÆÁ¦£¬×÷ÓþàÀëÓëµÚÒ»´ÎÏàͬ£¬ÔòÓÐ
${v}_{3}^{2}-{v}_{2}^{2}=2{a}_{1}{x}_{1}$
½âµÃv₃=$\frac{\sqrt{52}}{5}$m/s
´ËºóÔÚˮƽ·½Ïò½öÊÜĦ²ÁÁ¦×÷ÓÃ×öÔȼõËÙÔ˶¯£¬»¬ÐеÄ×î´ó¾àÀëΪ£º
${x}_{2}=\frac{0-{v}_{3}^{2}}{2{a}_{2}}$
½âµÃ£ºx₂=5.2m
´ð£º£¨1£©µÚÒ»´ÎÀûÓû¬Ñ©ÕȶÔÑ©Ãæ×÷ÓûñµÃµÄËٶȴóСΪ1.2m/s£¬Õâ¶Îʱ¼äÄÚµÄλÒÆΪ0.6m£»
£¨2£©¸ÃÔ˶¯Ô±£¨¿ÉÊÓΪÖʵ㣩µÚ¶þ´Î³·³ýˮƽÍÆÁ¦ºó»¬ÐеÄ×î´ó¾àÀëΪ5.2m£®

µãÆÀ ±¾Ì⿼²éÁËÅ£¶ÙµÚ¶þ¶¨ÂɺÍÔ˶¯Ñ§¹«Ê½µÄ×ÛºÏÔËÓ㬹ؼüÊÇ×¢Òâ·Ö¶Î½øÐд¦Àí£¬±¾ÌâÒ²¿ÉÒÔÀûÓö¯Á¿¶¨Àí½áºÏ¶¯Äܶ¨Àí½øÐÐÇó½â£®