: hm(f (x'y+x) f (x' il)= f(x)-f (o)
*Bei L21409 M1t sqi ddy kh6ng khiit taqng nQt diu ddy
kh6ng khiit taqng nQt diu ddy
.;
treo vdo tran nha, dau con lqi
bu6c vao vat m. Phia du'oi vQt m m
cd niji vdi vdt 2m th6ng qua m6t
ld xo. Ban ddu h€ 6 trqng thdi
cdn biing, dA bi€n dqng cila ld
xo khi do ld 3cm. Ngudi ta dem Znr
',!
dot so\ dav.
a) Tim gia t6c cila cac vQt ngay khi vira d6t day
b1 Sau bao lau ld xo lqi tro v€ trqng thdi ban ddu? Tim vdn t6c cua cdc vqt khi d6.
Ldi gidi. a) Khi chua d6t ddy, ld xo gi6n A/s .
Di6u kiQn cdn bing v6i vflt 2m ld kNo =21?8. Npay say khi d5t dAy, vi tri cdc v{t chua thay d6i, gia t6c cira cfrcvQt2mvdmllnlugtbing
^ k Llo 2mg
az:0'.at:J:-i=,f.
b) Sau khi dOt dAy, kh6i tdm G cta hq roi t.u do. Trong hq quy chi6u g6n voi G c6c vf,t sE
dao clQng di6u hoa nhu nhirng con l[c ld xo md dAu ld xo tucrng img g[n v6i G.
Khi chi0u dei ld xo ld, l, vQt m c6ch kh6i tdm al
G m6t khoins a. J-' cdnv6,t2m cSch kh6i t6m I
-. D0 cimg 1o xo tuong ring cua c6c con 16c
a'
J
mvd2mld fu vit k2.Tac6
k,.?! '3 '3 = k,.L : k.t = k, :Y 2 i k, = 3k.TAn so g6c cua hai con 6c lAn luqt li TAn so g6c cua hai con 6c lAn luqt li
trEl fh Ek
^ = l;= l*t*= l*= \*'
Nhu vdy hai vflt dao dQng cung t6n s6 g6c vd ngugc pha nhau.
Ld xo sE tro vd trqngthdiban dAu l6n ddu ti6n sau 1 chu ki dao dQng, tuc ld sau kho6ng thoi
sian T : zn ^E : 2n,P- = zn.$= o, 2s.
\fr, Vr !3s
Khi d6 vQn t6c ci-r- cdc vflt,ddi vOi,khOl tdm G
b[ng 0, vfln t6c c'ita c6c ddi vdi ddt bing vpn t6c cira tn6i tam G: v, = v, = gT:2m/s. A
FNnl" x6t. Chcb4n sau dAy c6 loi gidi t6t
Hii 2uong: Pham Thi Y€n Nhi, 11 Li, THPT chuy6n Nguyen Trdir Nam Dinh: Dinh'fiet Thdng, Bili Xudn Hidn. 12 Li, THPT chuy6n L€ HOng Phong; Hir Nam: Einh Ngpc Hdi, l\ Li, THPT chuy6n Bi6n Hda; NghQ Anz Trdn Vdn B(c, 12A6, THPT chuyOn DH Vinh; Qr4ng Ngdit Ki€u Vdn Bdo, 11 Li, THPT chuyCn L0 Khi6t; Binh Dintu Trdn Quang Khanh, 12TN2, THPT Tang B4t H6, Hodi Nhcrn; TP. H6 Chi islinh. Phqm Quang Dfing, l1 Li, PTNK DHQG TP. HO Chi Minh.
NGITYEN XUAN QUANG
TONN HQC