µÚÒ»´Î×÷Òµ½â´ð£Õñ¶¯
11-1 Ò»ÖÊÁ¿ÎªmµÄÖʵãÔÚÁ¦F = -?2xµÄ×÷ÓÃÏÂÑØxÖáÔ˶¯£®ÇóÆäÔ˶¯µÄÖÜÆÚ£®
½â£º½«F = -?2xÓëF = -kx±È½Ï£¬ÖªÖʵã×÷¼òгÕñ¶¯£¬
k= ?2£® k??ÓÖ ?? mm2? T??2m
m0Fx
?
11-2 ÖÊÁ¿Îª2 kgµÄÖʵ㣬°´·½³Ìx?0.2sin[5t?(?/6)] (SI)ÑØ×ÅxÖáÕñ¶¯£®Çó£º
(1) t = 0ʱ£¬×÷ÓÃÓÚÖʵãµÄÁ¦µÄ´óС£» (2) ×÷ÓÃÓÚÖʵãµÄÁ¦µÄ×î´óÖµºÍ´ËʱÖʵãµÄλÖã® ½â£º(1) t = 0ʱ£¬ a = 2.5 m/s2 £¬| F | = ma = 5 N (2) | amax | = 5£¬Æäʱ | sin(5t - ?/6) | = 1 | Fmax | = m| amax | = 10 N x = ¡À0.2 m£¨Õñ·ù¶Ëµã£©
11-15 Ò»ÎïÌå×÷¼òгÕñ¶¯£¬ÆäËÙ¶È×î´óÖµvm = 3310-2 m/s£¬ÆäÕñ·ùA = 2310-2 m£®Èôt = 0ʱ£¬ÎïÌåλÓÚÆ½ºâλÖÃÇÒÏòxÖáµÄ¸º·½ÏòÔ˶¯. Çó£º
(1) Õñ¶¯ÖÜÆÚT£» (2) ¼ÓËٶȵÄ×î´óÖµam £» (3) Õñ¶¯·½³ÌµÄÊýֵʽ£®
½â: (1) vm = ?A ¡à? = vm / A =1.5 s-1 ¡à T = 2?/????4.19 s
(2) am = ?2A = vm ?? = 4.5310-2 m/s2
1 (3) ???
21 x = 0.02cos(1.5t??) (SI)
2
11-24 Ò»ÎïÌåÖÊÁ¿Îª0.25 kg£¬ÔÚµ¯ÐÔÁ¦×÷ÓÃÏÂ×÷¼òгÕñ¶¯£¬µ¯»ÉµÄ¾¢¶ÈϵÊýk = 25 N2m-1£¬Èç¹ûÆðʼÕñ¶¯Ê±¾ßÓÐÊÆÄÜ0.06 JºÍ¶¯ÄÜ0.02 J£¬Çó (1) Õñ·ù£»
1
(2) ¶¯ÄÜÇ¡µÈÓÚÊÆÄÜʱµÄÎ»ÒÆ£»
(3) ¾¹ýƽºâλÖÃʱÎïÌåµÄËÙ¶È£®
1½â£º(1) E?EK?Ep?kA2
2 A?[2(EK?Ep)/k]1/2= 0.08 m
121kx?mv2 222 m?2x2?m?2A2sin(?t??)
(2)
2 x2?A2sin(?t??)?A2[1?cos2(?t??)]?A2?x2
2x2?A2£¬ x??A/2??0.0566 m (3) ¹ýƽºâµãʱ£¬x = 0£¬´Ëʱ¶¯ÄܵÈÓÚ×ÜÄÜÁ¿
1 E?EK?Ep?mv2
2 v?[2(EK?Ep)/m]1/2??0.8 m/s
11-29 Á½¸öͬ·½Ïò¼òгÕñ¶¯µÄÕñ¶¯·½³Ì·Ö±ðΪ
31 x1?5?10?2cos(10t??) (SI), x2?6?10?2cos(10t??) (SI)
44ÇóºÏÕñ¶¯·½³Ì£®
½â£ºÒÀºÏÕñ¶¯µÄÕñ·ù¼°³õÏ๫ʽ¿ÉµÃ
312?2A1A2co?s??52?62?2?5?6?cos(???)?10?2 m A?A12?A244 ?7.81?10?2 m
5sin3?(/4)?6sin?(/4) ??arctg = 84.8¡ã=1.48 rad
5cos3?(/4)?6cos?(/4)10t?1.48) (SI) ÔòËùÇóµÄºÏ³ÉÕñ¶¯·½³ÌΪ x?7.81?10?2cos(
11-30 Ò»ÎïÌåͬʱ²ÎÓëÁ½¸öͬ·½ÏòµÄ¼òгÕñ¶¯£º x1?0.04cos2?(t?1?) (SI), x2?0.03cos(2?t??) (SI)
2Çó´ËÎïÌåµÄÕñ¶¯·½³Ì£®
½â£ºÉèºÏ³ÉÔ˶¯£¨¼òгÕñ¶¯£©µÄÕñ¶¯·½³ÌΪ x?Acos?(t??)
2?2A1A2cos?2(??1) ¢Ù Ôò A2?A12?A2ÒÔ A1 = 4 cm£¬A2 = 3 cm£¬?2??1???1??1?´úÈë¢Ùʽ£¬µÃ
22 A?42?32cm?5 cm
Asin?1?A2sin?20.04?arctgÓÖ ??arctg1 ¢Ú
A1cos?1?A2cos?2?0.03 ¡Ö127¡ã¡Ö2.22 rad
¡à x?0.05cos(2?t?2.22) (SI)
2
µÚ¶þ´Î×÷Òµ½â´ð£²¨¶¯
12-2 Ò»Æ½Ãæ¼òг²¨ÑØxÖáÕýÏò´«²¥£¬²¨µÄÕñ·ùA = 10 cm£¬²¨µÄ½ÇƵÂÊ? = 7? rad/s.µ±t = 1.0 sʱ£¬x = 10 cm´¦µÄaÖʵãÕýͨ¹ýÆäƽºâλÖÃÏòyÖḺ·½ÏòÔ˶¯£¬¶øx = 20 cm´¦µÄbÖʵãÕýͨ¹ýy = 5.0 cmµãÏòyÖáÕý·½ÏòÔ˶¯£®Éè¸Ã²¨²¨³¤? >10 cm£¬Çó¸ÃÆ½Ãæ²¨µÄ±í´ïʽ£®
½â£ºÉèÆ½Ãæ¼òг²¨µÄ²¨³¤Îª?£¬×ø±êԵ㴦ÖʵãÕñ¶¯³õÏàΪ?£¬Ôò¸ÃÁÐÆ½Ãæ¼òг²¨µÄ±í´ïʽ¿Éд³É y?0.1cos7?(t?2?x/???) (SI) t = 1 sʱ y?0.1cos7?[?2?(0.1/?)??]?0 Òò´ËʱaÖʵãÏòyÖḺ·½ÏòÔ˶¯£¬¹Ê
1? ¢Ù 2¶ø´Ëʱ£¬bÖʵãÕýͨ¹ýy = 0.05 m´¦ÏòyÖáÕý·½ÏòÔ˶¯£¬Ó¦ÓÐ y?0.1cos[7??2?(0.2/?)??]?0.05
1ÇÒ 7??2?(0.2/?)????? ¢Ú
3ÓÉ¢Ù¡¢¢ÚÁ½Ê½ÁªÁ¢µÃ ?? = 0.24 m ???17?/3
7??2?(0.1/?)???¡à ¸ÃÆ½Ãæ¼òг²¨µÄ±í´ïʽΪ
?x17??] (SI) 0.123?x1»ò y?0.1cos[7?t???] (SI)
0.123
12-4 Ò»ÁÐÆ½Ãæ¼òг²¨ÔÚýÖÊÖÐÒÔ²¨ËÙu = 5 m/sÑØy (cm) y?0.1cos[7?t?xÖáÕýÏò´«²¥£¬ÔµãO´¦ÖÊÔªµÄÕñ¶¯ÇúÏßÈçͼËùʾ£® (1) Çó½â²¢»³öx = 25 m´¦ÖÊÔªµÄÕñ¶¯ÇúÏߣ® (2) Çó½â²¢»³öt = 3 sʱµÄ²¨ÐÎÇúÏߣ®
2O24t (s)
½â£º(1) ÔµãO´¦ÖÊÔªµÄÕñ¶¯·½³ÌΪ
11 y?2?10?2cos(?t??)£¬ (SI)
2211²¨µÄ±í´ïʽΪ y?2?10?2cos(?(t?x/5)??)£¬ (SI)
22 x = 25 m´¦ÖÊÔªµÄÕñ¶¯·½³ÌΪ
1 y?2?10?2cos(?t?3?)£¬ (SI)
2Õñ¶¯ÇúÏß¼ûͼ (a)
(2) t = 3 sʱµÄ²¨ÐÎÇúÏß·½³Ì
3
y?2?10?2cos(???x/10)£¬ (SI) ²¨ÐÎÇúÏß¼ûͼ
y (m)2310-2y (m)u510152025x (m)O1234-2310-2t (s)O(a) (b)
12-15 Ò»Æ½Ãæ¼òг²¨£¬ÆµÂÊΪ300 Hz£¬²¨ËÙΪ340 m/s£¬ÔÚ½ØÃæÃæ»ýΪ3.00310-2 m2µÄ¹ÜÄÚ¿ÕÆøÖд«²¥£¬ÈôÔÚ10 sÄÚͨ¹ý½ØÃæµÄÄÜÁ¿Îª2.70310-2 J£¬Çó (1) ͨ¹ý½ØÃæµÄƽ¾ùÄÜÁ÷£» (2) ²¨µÄƽ¾ùÄÜÁ÷Ãܶȣ» (3) ²¨µÄƽ¾ùÄÜÁ¿Ãܶȣ®
½â£º(1) P?W/t?2.70310-3 J/s
(2) I?P/S?9.00310-2 J /(s2m2) (3) I?w?u
ã w?I/u?2.65310-4 J/m3
12-18 ÈçͼËùʾ£¬Á½Ïà¸É²¨Ô´ÔÚxÖáÉϵÄλÖÃΪ
S1ºÍS2£¬Æä¼ä¾àÀëΪd = 30 m£¬S1λÓÚ×ø±êÔµãO£®ÉèO x1 x2 x S1 S2 ²¨Ö»ÑØxÖáÕý¸º·½Ïò´«²¥£¬µ¥¶À´«²¥Ê±Ç¿¶È±£³Ö²»
d ±ä£®x1 = 9 m ºÍx2 = 12 m´¦µÄÁ½µãÊÇÏàÁÚµÄÁ½¸öÒò¸É Éæ¶ø¾²Ö¹µÄµã£®ÇóÁ½²¨µÄ²¨³¤ºÍÁ½²¨Ô´¼ä×îСÏàλ²î£®
½â£ºÉèS1ºÍS2µÄÕñ¶¯Ïàλ·Ö±ðΪ??1ºÍ??2£®ÔÚx1µãÁ½²¨ÒýÆðµÄÕñ¶¯Ïàλ²î
d?x1x]?[?1?2?1]?(2K?1)? [?2?2?
??¼´ (?2??1)?2?d?2x1??(2K?1)? ¢Ù
ÔÚx2µãÁ½²¨ÒýÆðµÄÕñ¶¯Ïàλ²î d?x2x]?[?1?2?2]?(2K?3)? [?2?2???¼´ (?2??1)?2?d?2x2?¢Ú£¢ÙµÃ 4?(x2?x1)/??2? ??2(x2?x1)?6 m
ÓÉ¢Ù ?2??1?(2K?1)??2??(2K?3)? ¢Ú
d?2x1??(2K?5)?
µ±K = -2¡¢-3ʱÏàλ²î×îС ?2??1???¡£
4