cuQn ddy kh6ng co tli6n tr0 thuan h
,r2 rrt2 fV
,,, - Lro .-c''o ---/o : Unrli = 0,024(A).
yr
- 2 - 2 +,1)- "rv/ -v)v,t
Do cuQn d0y c6 diQn trd thudn n6n cdng suAt
toi nhiQt tr6n cuQn d0y ndy bdng
_1
P = rI2 =,(+)- \\t L) = +,fi = +.0,s.(o,oz+)2:0,43(mSD. :0,43(mSD.
Vpy, dO duy tri dao clQrg thi phni cung c6p cho
m4ch mdt c6ng su0t bdng 0,43mW.o
DANG 3. Chfrng minh mQt vft dao tlQng
didiu hoi
Phwong phtrt:p gidl - CAn chimg minh ring li
dO cira vflt trong dao dQng co (hay diQn tich,
higu dign th6, culng dQ dong di6n trong dao
dQng diQn tu) duqc bi6u diSn qua hdm sin
ho{c c6sin.
- Chrmg minh ring li d0 cria vQt (hay diQn tich tr6n m6i ban tu tli6n trong m4ch dao dQ."g ZO
thoi mdn phucrng trinh cira dao dQng di6u hod
d2x ) ^ , q2q --z-.
:-++ dt' lr'x =0 hay ++o'q :0.
dt'
- Chtmg minhr5ng lUc t6ng hqp tic dqng ltu vflt
c6 dang lyc k6ov0 F = -l<x (xldlid0 cuavpt).
*Thi dU 5. MOt khtic gd lri"ry trw c6 khtii
luqng m, di€n tich ctdy ld S, n6i trong nunc.
Truc hinh tru c6 phwong thdng &img. Nhdn
khrtc gd chim vdo nuoc mQt dogn nhd x so voi
vi tri cdn bdng r6i thd nhe tay cho vQt dao
dQng. Bi& kh6i lm. ng ridng crta nuoc ld P, gia
dc ffpng trudng ld g.
a) Chamg minh khuc 96 dao d\ng diiu hod. b) Tinh chu ki dao dQng cila khuc 96.
Hrdng djn gidl a).Chon truc.toa dQ Oxhu6ng thEng drmg xu6ng ducri, g6c O it vi tn hu6ng thEng drmg xu6ng ducri, g6c O it vi tn
cdn bang .ru tt,i. g5. rpl vi hi cdn bing,
khic g6-chiu tac dpng cira hai luc cin bing
nhau: trgng lpc P cria khirc 96 huong xu6ng
ducri, luc dAy Acsimet il hu6ng 16n tr6n.
Phucrng trinh dinh luflt II Newton cho vflt ld
P+Fu:g (1)
Chi0u phucrng trinh (1) l6n trUc Ox,ta cb
P-Fd =0 <> F.t=P.
Khi vat chim sdu th6m khoi vi tri cdn bing mQt ilopn x thi lgc dAy Acsimet l6n hon hqng lpc
mQtlugng P = -pSxg.
D?t k = pSg, suy ra F = -lu (2) Phuong trinh (2) ld lUc k6o v6. VQy ktlic g6
dao dQng di6u hod.
b) Tt (2)tac6
"Y - d2x k
-lu - F : mo-i r',r, - ^ *--v: o.
dt' - dt' m
n k -. d2s
Ddt 'mdt"<o' = - thi -* * ot2x = 0.
Chuki dao tlQng
^-
T_L.lL_a*
a- (D
*Thi dq 6. MQt bdn cqc cria t1r diQn phdng c6
khiit luqng m, di€n tich S duqc treo vdo mQt ctiu ct)a ld xo c6 dq cilmg k, dd.u kia da ld xo dtrqc gan vdo gid ,6 dinh, bdn cqc kia duqc
giu cO dinh. Khodng cdch gitra hai bdn cqrc.d
lna aie* ban diu ta a. ttai fu iti€n voi nguin
di€n m\t chiiu trong thdi gian ngdn de no fich di€n d€n hi€u di€n thA U. H€ th6nl daqc ddt trong kh6ng khi.
a) Chilmg td riing bdn cqc tu ili€n duqc treo vdo ld xo dao dong diiu hod.
b) DO c*ng k ct)a ld xo phdi bdng bao nhi€u dd
kh6ng xdy ra sq ti€p xuc giica cdc bdn arc?
Hrdng ddn gidl a) Khi gifta hai bAn cgc tir
diQn c6 hieu diQn th6, U, bin tr"r diQn dugc n6i
v6i ld xo (ggi li bin tr6n) chiu t6c dqng qia ba
lgc: trong lgc cira bhn F, luc diQn truong
4 = qE vd lgc ddn hOi cira lo *o 7j. Cia
sti bdn cgc duoi tich ttiQn 6m, thi F,4,., ,.,
huong xudng duoi, cdn Fa1, hu(mg l6n tr6n.
huong xudng duoi, cdn Fa1, hu(mg l6n tr6n.
mg+qE-kLls=g (1)
f;
t/otr "