Question

7£®ÈçͼËùʾ£¬¹â»¬°ëÔ²ÐιìµÀ°ë¾¶Îªr=0.4m£¬BCΪÊúÖ±Ö±¾¶£¬AΪ°ëÔ²ÐιìµÀÉÏÓëÔ²ÐÄOµÈ¸ßµÄλÖã®Ò»ÖÊÁ¿Îªm=2.0kgµÄСÇò£¨¿ÉÊÓΪÖʵ㣩×ÔA´¦ÒÔijһÊúÖ±ÏòϵijõËٶȻ¬Ï£¬½øÈëÓëCµãÏàÇеĴֲÚˮƽÃæCDÉÏ£¬ÔÚˮƽ»¬µÀÉÏÓÐÒ»ÇáÖʵ¯»É£¬ÆäÒ»¶Ë¹Ì¶¨ÔÚÊúֱǽÉÏ£¬ÁíÒ»¶ËλÓÚ»¬µÀÄ©¶ËµÄCµã£¨´Ëʱµ¯»É´¦ÓÚ×ÔȻ״̬£©£®ÈôСÇòÓëˮƽ»¬µÀ¼äµÄ¶¯Ä¦²ÁÒòÊý¦Ì=0.5£¬µ¯»É±»Ñ¹ËõµÄ×î´ó³¤¶ÈΪ0.2m£®Ð¡ÇòÇᵯ»É·´µ¯ºóÇ¡ºÃÄÜͨ¹ý°ëÔ²ÐιìµÀµÄ×î¸ßµãB£¬ÖØÁ¦¼ÓËÙ¶Èg=10m/s²£¬ÔòÏÂÁÐ˵·¨ÖÐÕýÈ·µÄÊÇ£¨¡¡¡¡£©

• A£® СÇòͨ¹ý×î¸ßµãBʱµÄËٶȴóСΪ2m/s
• B£® СÇòÔ˶¯¹ý³ÌÖÐ×ܵ¯»ÉµÄ×î´óµ¯ÐÔÊÆÄÜΪ20J
• C£® СÇò´ÓAµãÊúÖÊÏ»¬µÄ³õËٶȴóСΪ4m/s
• D£® СÇòµÚÒ»´Î¾­¹ýCµãʱ¶ÔCµãµÄѹÁ¦Îª120N

Answer 1

·ÖÎö ÔÚ×î¸ßµã£¬ÊÇÖØÁ¦ÌṩÏòÐÄÁ¦£¬¸ù¾ÝÅ£¶ÙµÚ¶þ¶¨ÂÉÁÐʽÇó½â×î¸ßµãBʱµÄËٶȣ»
¶Ô·´µ¯ºó¹ý³Ì¸ù¾Ý¶¯Äܶ¨ÀíÁÐʽ¿ÉÒÔÇó½âµ¯»ÉµÄ×î´óµ¯ÐÔÊÆÄÜ£»
¶ÔÏ»¬¹ý³Ì¸ù¾Ý¶¯Äܶ¨ÀíÁÐʽÇó½â³õËٶȣ»
ÔÚCµã£¬ÖØÁ¦ºÍÖ§³ÖÁ¦µÄºÏÁ¦ÌṩÏòÐÄÁ¦£®

½â´ð ½â£ºA¡¢Ð¡Çò±»Çᵯ»É·´µ¯ºóÇ¡ºÃÄÜͨ¹ý°ëÔ²ÐιìµÀµÄ×î¸ßµãB£¬¹ÊÔÚBµãÊÇÖØÁ¦ÌṩÏòÐÄÁ¦£¬¹Ê£º
mg=m$\frac{{v}^{2}}{r}$
½âµÃ£º
v=$\sqrt{gr}$=$\sqrt{10¡Á0.4}=2m/s$
¹ÊAÕýÈ·£»
B¡¢¶Ô·´µ¯ºóµ½×î¸ßµãµÄ¹ý³Ì¸ù¾Ý¶¯Äܶ¨Àí£¬ÓУº
W_µ¯-¦Ìmgx-mg£¨2R£©=$\frac{1}{2}m{v}^{2}-0$
ÆäÖУº
W_µ¯=E_pm
ÁªÁ¢½âµÃ£º
E_pm=¦Ìmgx+mg£¨2r£©+$\frac{1}{2}m{v}^{2}$=0.5¡Á2¡Á10¡Á0.2+2¡Á10¡Á£¨2¡Á0.4£©+$\frac{1}{2}¡Á2¡Á{2}^{2}$=22J
¹ÊB´íÎó£»
C¡¢¶ÔÔ˶¯È«³Ì£¬¸ù¾Ý¶¯Äܶ¨Àí£¬ÓУº
-mgr-2¦Ìmgx=$\frac{1}{2}m{v}^{2}-\frac{1}{2}m{v}_{0}^{2}$
½âµÃ£º
v₀=$\sqrt{{v}^{2}+2£¨gr+2¦Ìgx£©}$=4m/s
¹ÊCÕýÈ·£»
D¡¢´ÓAµ½C£¬¸ù¾Ý¶¯Äܶ¨Àí£¬ÓУº
mgr=$\frac{1}{2}m{v}_{C}^{2}-\frac{1}{2}m{v}_{0}^{2}$
½âµÃ£º
${v}_{C}=\sqrt{{v}_{0}^{2}+2gr}$=$\sqrt{14+2¡Á10¡Á0.4}$=4$\sqrt{2}$m/s
ÔÚCµã£¬¸ù¾ÝÅ£¶ÙµÚ¶þ¶¨ÂÉ£¬ÓУº
F-mg=m$\frac{{v}_{C}^{2}}{r}$
½âµÃ£º
F=mg+m$\frac{{v}_{C}^{2}}{r}$=2¡Á10+2¡Á$\frac{32}{0.4}$=180N
¹ÊD´íÎó£»
¹ÊÑ¡£ºAC£®

µãÆÀ ±¾Ìâ¹Ø¼üÊÇÒªÃ÷ȷСÇòµÄÔ˶¯Çé¿ö¡¢ÊÜÁ¦Çé¿öºÍÄÜÁ¿×ª»¯Çé¿ö£¬½áºÏ¶¯Äܶ¨Àí¡¢ÏòÐÄÁ¦¹«Ê½ºÍÅ£¶ÙµÚ¶þ¶¨ÂÉÁÐʽ·ÖÎö£¬Áé»îÑ¡Ôñ¹ý³ÌºÍ״̬Êǹؼü£®