Question

7£®ÈçͼËùʾ£¬ÖÊÁ¿M=8kgµÄС³µ·ÅÔÚˮƽ¹â»¬µÄƽÃæÉÏ£¬ÔÚС³µ×ó¶Ë¼ÓһˮƽÍÆÁ¦F=8N£¬µ±Ð¡³µÏòÓÒÔ˶¯µÄËٶȴﵽ1.5m/sʱ£¬ÔÚС³µÓÒ¶ËÇáÇáµØ·ÅÉÏÒ»¸ö´óС²»¼Æ£¬ÖÊÁ¿Îªm=2kgµÄú¿é£¬Ãº¿éÓëС³µ¼äµÄ¶¯Ä¦²ÁÒòÊýΪ0.2£¬Ð¡³µ×ã¹»³¤£¬È¡g=10m/s2£®Ç󣺴Óú¿é·ÅÉÏË®Éϳµ¿ªÊ¼£®
£¨1£©¾­¶à³¤Ê±¼äÁ½Õß´ïµ½ÏàͬµÄËٶȣ»
£¨2£©¾­¹ýt=1.5sú¿éͨ¹ýµÄλÒÆ´óС£»
£¨3£©Ãº¿éÔÚС³µÉÏÁô϶೤µÄºÛ¼££®

Answer 1

·ÖÎö £¨1£©¸ù¾ÝËÙ¶Èʱ¼ä¹«Ê½Çó³öСÎï¿éºÍС³µËÙ¶ÈÏàͬʱËùÐèµÄʱ¼ä£»
£¨2£©Ð¡Îï¿éºÍС³µ´ïµ½¹²Í¬ËٶȺó£¬Ò»Æð×öÔȼÓËÙÖ±ÏßÔ˶¯£¬¸ù¾ÝÅ£¶ÙµÚ¶þ¶¨ÂÉÇó³öËÙ¶ÈÏàͬºóµÄ¼ÓËٶȣ¬ÔËÓÃÔ˶¯Ñ§¹«Ê½·Ö±ðÇó³öËÙ¶ÈÏàµÈÇ°ºÍËÙ¶ÈÏàµÈºó£¬Ð¡Îï¿éµÄλÒÆ£¬´Ó¶øµÃ³öСÎï¿éµÄ×ÜλÒÆ£®
£¨3£©ËÙ¶ÈÏàµÈÇ°Á½ÕßµÄλÒƲΪú¿éÔÚС³µÉÏÁôϵĺۼ££¬½áºÏλÒƹ«Ê½Çó³öÁ½Õß·¢ÉúµÄÏà¶ÔλÒÆ£¬¼´¿ÉÇó½â£®

½â´ð ½â£º£¨1£©Îï¿éµÄ¼ÓËÙ¶ÈΪ£ºa_m=$\frac{f}{m}$=¦Ìg=0.2¡Á10=2m/s²£¬
С³µµÄ¼ÓËٶȣº${a}_{M}^{\;}=\frac{F-¦Ìmg}{M}=\frac{8-0.2¡Á20}{8}=0.5m/{s}_{\;}^{2}$
ËÙ¶ÈÏàµÈʱ£¬ÓÉa_mt=v₀+a_MtµÃ£º
$t=\frac{1.5}{2-0.5}=1s$             
£¨2£©ÔÚ¿ªÊ¼1sÄÚСÎï¿éµÄλÒÆ£º${s}_{1}^{\;}=\frac{1}{2}{a}_{m}^{\;}{t}_{\;}^{2}=\frac{1}{2}¡Á2¡Á1=1m$
×î´óËٶȣºv=a_mt=2¡Á1m/s=2m/s£®
ÔÚ½ÓÏÂÀ´µÄ0.5sÎï¿éÓëС³µÏà¶Ô¾²Ö¹£¬Ò»Æð×ö¼ÓËÙÔ˶¯
ÇÒ¼ÓËٶȣº$a=\frac{F}{m+M}=0.8m/{s}_{\;}^{2}$
Õâ0.5sÄÚµÄλÒÆ£º${s}_{2}^{\;}=vt+\frac{1}{2}a{t}_{\;}^{2}=2¡Á0.5+\frac{1}{2}¡Á0.8¡Á0£®{5}_{\;}^{2}$=1.1m
¾­¹ýt=1.5 sСÎï¿éͨ¹ýµÄ×ÜλÒÆ£ºs=s₁+s₂=2.1m£®
£¨3£©ËÙ¶ÈÏàµÈʱ£¬Ð¡Îï¿é£º${s}_{1}^{\;}=\frac{1}{2}{a}_{m}^{\;}{t}_{\;}^{\;}=\frac{1}{2}¡Á2¡Á{1}_{\;}^{2}=1m$     
С³µ£º${s}_{2}^{\;}={v}_{0}^{\;}t+\frac{1}{2}{a}_{M}^{\;}{t}_{\;}^{2}$=$1.5¡Á1+\frac{1}{2}¡Á0.5¡Á{1}_{\;}^{2}=1.75m$
ºÛ¼£³¤¶È£ºx=S₂-S₁=1.75-1=0.75m   
´ð£º£¨1£©¾­1sʱ¼äÁ½Õß´ïµ½ÏàͬµÄËٶȣ®
£¨2£©´ÓСÎï¿é·ÅÉÏС³µ¿ªÊ¼£¬¾­¹ýt=1.5sСÎï¿éͨ¹ýµÄλÒÆ´óСΪ2.1m£®
£¨3£©Ãº¿éÔÚС³µÉÏÁôÏÂ0.75m³¤µÄºÛ¼££®

µãÆÀ ½â¾ö±¾ÌâµÄ¹Ø¼üÀíÇåСÎï¿éºÍС³µµÄÔ˶¯µÄÇé¿ö£¬½áºÏÅ£¶ÙµÚ¶þ¶¨ÂɺÍÔ˶¯Ñ§¹«Ê½Áé»îÇó½â£®