FBC?2F1
(2) È¡½ÂÁ´CΪÑо¿¶ÔÏó£¬BC¡¢CD¾ùΪ¶þÁ¦¸Ë£¬»ÊÜÁ¦Í¼ºÍ·â±ÕÁ¦Èý½ÇÐΣ»
FCB C F2 FCD
FCB FCD
F2
FCB?F2cos30o?ÓÉǰ¶þʽ¿ÉµÃ£º
3F2 2FBC?FCB 2F1??F1?3F226F2?0.61F2 or F2?1.63F14
2-9 Èý¸ù²»¼ÆÖØÁ¿µÄ¸ËAB£¬AC£¬ADÔÚAµãÓýÂÁ´Á¬½Ó£¬¸÷¸ËÓëË®Æ½ÃæµÄ¼Ð½Ç·Ö±ðΪ450£¬
450ºÍ600£¬ÈçͼËùʾ¡£ÊÔÇóÔÚÓëODƽÐеÄÁ¦F×÷ÓÃÏ£¬¸÷¸ËËùÊܵÄÁ¦¡£ÒÑÖªF=0.6 kN¡£
z £¬
FAB B A F 45o O 45o 60o FAD D C FAC x y ½â£º(1) È¡ÕûÌåΪÑо¿¶ÔÏó£¬ÊÜÁ¦·ÖÎö£¬AB¡¢AB¡¢AD¾ùΪ¶þÁ¦¸Ë£¬»ÊÜÁ¦Í¼£¬µÃµ½Ò»¸ö¿Õ
¼ä»ã½»Á¦Ïµ£» (2) ÁÐÆ½ºâ·½³Ì£º
ooF?0 F?cos45? F?cos45?0?xACAB?F?F½âµÃ£º
y?0 F?FADcos60o?0?0 FADsin60o?FACsin45o?FABsin45o?0
zFAD?2F?1.2 kN FAC?FAB?AB¡¢AC¸ËÊÜÀ£¬AD¸ËÊÜѹ¡£
6FAD?0.735 kN 4
8
3-1 ÒÑÖªÁºABÉÏ×÷ÓÃÒ»Á¦Å¼£¬Á¦Å¼¾ØÎªM£¬Áº³¤Îªl£¬ÁºÖز»¼Æ¡£ÇóÔÚͼa£¬b£¬cÈýÖÖÇé
¿öÏ£¬Ö§×ùAºÍBµÄÔ¼ÊøÁ¦
l/2 M l/3 M A B A B
l l (a) (b)
l/2 M B A ¦È l
(c)
½â£º(a) ÊÜÁ¦·ÖÎö£¬»ÊÜÁ¦Í¼£»A¡¢B´¦µÄÔ¼ÊøÁ¦×é³ÉÒ»¸öÁ¦Å¼£» l/2 M A B
FA l FB
ÁÐÆ½ºâ·½³Ì£º
?M?0 FMB?l?M?0 FB?l
?FMA?FB?l(b) ÊÜÁ¦·ÖÎö£¬»ÊÜÁ¦Í¼£»A¡¢B´¦µÄÔ¼ÊøÁ¦×é³ÉÒ»¸öÁ¦Å¼£»
l/3 M A B
FA l FB
ÁÐÆ½ºâ·½³Ì£º
?M?0 FB?l?M?0 FMB?l
?F?MA?FBl (c) ÊÜÁ¦·ÖÎö£¬»ÊÜÁ¦Í¼£»A¡¢B´¦µÄÔ¼ÊøÁ¦×é³ÉÒ»¸öÁ¦Å¼£»
FA l/2 M
A B ¦È l FB
9
ÁÐÆ½ºâ·½³Ì£º
?M?0 FB?l?cos??M?0 FB?M?FA?FB?lcos?Mlcos?
3-2 ÔÚÌâͼËùʾ½á¹¹ÖжþÇú¸Ë×ÔÖØ²»¼Æ£¬Çú¸ËABÉÏ×÷ÓÃÓÐÖ÷¶¯Á¦Å¼£¬ÆäÁ¦Å¼¾ØÎªM£¬ÊÔÇó
AºÍCµã´¦µÄÔ¼ÊøÁ¦¡£
a
A 3a B a C Ma
½â£º(1) È¡BCΪÑо¿¶ÔÏó£¬ÊÜÁ¦·ÖÎö£¬BCΪ¶þÁ¦¸Ë£¬»ÊÜÁ¦Í¼£» F
B
B C FC
FB?FC
(2) È¡ABΪÑо¿¶ÔÏó£¬ÊÜÁ¦·ÖÎö£¬A¡¢BµÄÔ¼ÊøÁ¦×é³ÉÒ»¸öÁ¦Å¼£¬»ÊÜÁ¦Í¼£»
B
FA A MF¡¯B 2'MM'FB??3a?a??M?0 FB??0.3542a 22aM?FA?FC?0.354a?M?0 3-3 ³ÝÂÖÏäµÄÁ½¸öÖáÉÏ×÷ÓõÄÁ¦Å¼ÈçÌâͼËùʾ£¬ËüÃǵÄÁ¦Å¼¾ØµÄ´óС·Ö±ðΪM1=500 Nm£¬
M2 =125 Nm¡£ÇóÁ½ÂÝ˨´¦µÄǦ´¹Ô¼ÊøÁ¦¡£Í¼Öг¤¶Èµ¥Î»Îªcm¡£
10
A M1 M2 B FA FB 50
½â£º(1) È¡ÕûÌåΪÑо¿¶ÔÏó£¬ÊÜÁ¦·ÖÎö£¬A¡¢BµÄÔ¼ÊøÁ¦×é³ÉÒ»¸öÁ¦Å¼£¬»ÊÜÁ¦Í¼£»
(2) ÁÐÆ½ºâ·½³Ì£º
?M?0 FB?l?M1?M2?0 FB??FA?FB?750 NM1?M2500?125??750 N l503-5 ËÄÁ¬¸Ë»ú¹¹ÔÚͼʾλÖÃÆ½ºâ¡£ÒÑÖªOA=60cm£¬BC=40cm£¬×÷ÓÃBCÉϵÄÁ¦Å¼µÄÁ¦Å¼¾Ø
´óСΪM2=1N.m£¬ÊÔÇó×÷ÓÃÔÚOAÉÏÁ¦Å¼µÄÁ¦Å¼¾Ø´óСM1ºÍABËùÊܵÄÁ¦FABËùÊܵÄÁ¦¡£¸÷¸ËÖØÁ¿²»¼Æ¡£
O M1 A C 30o B
M2 ½â£º(1) Ñо¿BC¸Ë£¬ÊÜÁ¦·ÖÎö£¬»ÊÜÁ¦Í¼£º
ÁÐÆ½ºâ·½³Ì£º
30 oB FC C M2 FB
?M?0 FB?BCsin30o?M2?0 M21FB???5 Noo0.4?sin30BCsin30(2) Ñо¿AB£¨¶þÁ¦¸Ë£©£¬ÊÜÁ¦Èçͼ£º
¿ÉÖª£º
''FA?FB?FB?5 N
F¡¯A A B F¡¯B (3) Ñо¿OA¸Ë£¬ÊÜÁ¦·ÖÎö£¬»ÊÜÁ¦Í¼£º
11