Giai Chi Tiet 2013 426
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Transcript of Giai Chi Tiet 2013 426
-
Trn Thanh Sn H Kin Trc HN
Cng hc tp trao i kin thc ,ti liu vt l www.facebook.com/eno.pro.5 ; [email protected] 1
I.Phn chung cho tt c th sinh Cu 1: t in p
0u U cos t (V) (vi 0U v khng i) vo hai u on mch gm cun dy khng thun
cm mc ni tip vi t in c in dung C (thay i c). Khi C = 0C th cng dng in trong mch sm
pha hn u l 1 ( 10
2
) v in p hiu dng hai u cun dy l 45V. Khi C=3
0C th cng dng in
trong mch tr pha hn u l 2 1
2
v in p hiu dng hai u cun dy l 135V. Gi tr ca U0 gn gi tr
no nht sau y? A. 95V. B. 75V. C. 64V. D. 130V.
HD: Nhn thy
+ 1 0C C v 2 03C C 1 23C CZ Z
+ 1 45dU V v 2 135dU V 2 13d dU U 2 13I I 1 23Z Z 2
2 2 2 11( ) 9
3
CL C L
ZR Z Z R Z
Gii ci phng trnh th c mi lin h : 2 2 1
2
L CL
Z ZR Z (1)
+ Nhn thy 2 12
hay 2 1
2
+ p dng h thc 1 2tan .tan 1
1
1 3. 1
CL
L C
ZZ
Z Z
R R
21
1( )3
CL C L
ZZ Z Z R
Gii phng trnh ny 1 15
0 2,53 6
C LC L
Z ZZ Z (2)
+ Th (2) vo (1) 2LZ R v 1 5CZ R
+ C 221 1
1 1 1 12 2
. . .d d L Cd L
U UU I Z Z R Z Z
Z R Z
. Thay ht cc d liu tm c
1 2 45 2( )dU U V 0 90U V
Cu 2: Trong mt th nghim Y-ng v giao thoa nh sng, bc sng nh sng n sc l 600 nm, khong cch gia hai khe hp l 1 mm. Khong cch t mt phng cha hai khe n mn quan st l 2 m. Khong vn quan st c trn mn c gi tr bng A. 1,2 mm B. 1,5 mm C. 0,9 mm D. 0,3 mm
HD: D
ia
=1,2mm
Cu 3: Trong th nghim Y-ng v giao thoa nh sng, nu thay nh sng n sc mu lam bng nh sng n sc mu vng v gi nguyn cc iu kin khc th trn mn quan st A. khong vn khng thay i B. khong vn tng ln C. v tr vn trung tm thay i D. khong vn gim xung
HD : Do Vng ngLam V Lami i
Cu 4: Sng in t c tn s 10 MHz truyn trong chn khng vi bc sng l A. 60m B. 6 m C. 30 m D. 3 m
HD: 1CKn c c c
v f f
=30m
Cu 5: t in p u = 120 2 cos2 ft (V) (f thay i c) vo hai u on mch mc ni tip gm cun cm thun c t cm L, in tr R v t in c in dng C, vi CR2 < 2L. Khi f = f1 th in p hiu dng gia hai
M thi 426
GII CHI TIT THI I HC NM 2012 2013 MN VT L
Thi gian lm bi : 90 pht
-
Trn Thanh Sn H Kin Trc HN
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u t in t cc i. Khi f = f2 = 1f 2 th in p hiu dng gia hai u in tr t cc i. Khi f = f3 th in
p hiu dng gia hai u cun cm t cc i ULmax. Gi tr ca ULmax gn gi tr no nht sau y? A. 173 V B. 57 V C. 145 V D. 85 V.
HD : p dng CT
2 22
0
2
max
1L L
U
U
22
2 21C
LMAX L
fU
U f (*)
Li c CT : 2
3 1 2.f f f 3 12f f hay 2L Cf f
Ri thay vo (*) 138,56LU V Cu 6 : Mt vt nh dao ng iu ha dc theo trc Ox vi bin 5 cm, chu k 2 s. Ti thi im t = 0, vt i qua cn bng O theo chiu dng. Phng trnh dao ng ca vt l
A. x 5cos( t )2
(cm) B. x 5cos(2 t )
2
(cm)
C. x 5cos(2 t )2
(cm) D. x 5cos( t )
2
(cm)
Hd:2
T
= ;
5cos( ) 00
5 sin( ) 0
x tt
v t
2
Cu 7: Ni hai cc ca mt my pht in xoay chiu mt pha vo hai u on mch A, B mc ni tip gm in
tr 69,1 , cun cm thun c t cm L v t in c in dung 176,8 F . B qua in tr thun ca cc cun
dy ca my pht. Bit rto my pht c hai cp cc. Khi rto quay u vi tc 1n 1350 vng/pht hoc
2n 1800 vng/pht th cng sut tiu th ca on mch AB l nh nhau. t cm L c gi tr gn gi tr no
nht sau y? A. 0,8 H. B. 0,7 H. C. 0,6 H. D. 0,2 H.
HD:1 1800n vng/fut =22,5vng/s 1 45f Hz ; 2 1800n vng/fut=30 vng/s
V 1 20CZ . Ta C f np n E n LZ n Nhng
1CZ
n
Th vo v gii nu bn ra c nh ny l thnh cng
2
1 1 110,9375 14 33423,67 0C L CZ Z Z . Thay s 1 134,868LZ
0,477( )L H
Cu 8 : Mt vt nh dao ng iu ha theo mt qu o thng di 12 cm. Dao ng ny c bin l A. 3 cm. B. 24 cm. C. 6 cm. D. 12 cm.
Cu 9: Mt ht c khi lng ngh m0. Theo thuyt tng i, khi lng ng (khi lng tng i tnh) ca ht ny khi chuyn ng vi tc 0,6 c (c l tc nh sng trong chn khng) l A. 1,25 m0. B. 0,36 m0 C. 1,75 m0 D. 0,25m0
HD: ADCT 0 0
02 2
2
1,251 0,6
1
m mm m
v
c
Cu 10: Mt con lc l xo gm vt nh c khi lng 100g v l xo c cng 40 N/m c t trn mt phng ngang khng ma st. Vt nh ang nm yn v tr cn bng, ti t = 0, tc dng lc F = 2 N ln vt nh (hnh v)
cho con lc dao ng iu ha n thi im t3
s th ngng tc dng lc F. Dao ng iu ha ca con lc sau
khi khng cn lc F tc dng c gi tr bin gn gi tr no nht sau y?
C 2 1
4
3n n
2 1
2 1
4
3
3
4
L L
C C
Z Z
Z Z
v
2 1
4
3E E
Li c 1 2P P
2 2
1 2I I
2 2
1 2
2 22 2 2 21 1 2 2L C L C
E E
R Z Z R Z Z
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Trn Thanh Sn H Kin Trc HN
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A. 9 cm. B. 11 cm. C. 5 cm. D. 7 cm.
Hd: Cu ny hi kh tng tng Ti t = 0 vt ang ng yn VTCB , ri cng ti y tc dng lc F ln vt , hy tng tng nh l 1 CLLX thng ng khi t=0 vt ang ng yn VTCB ri sau theo thm vt nng vo th r rng n s b dn thm 1
on l l , th bi ny cng th lc F s lm cho l xo dn ra 1 on l =F/ k = 5cm v y s l VTCB O2 mi
ca vt v n s dh vi bin A2 no . Tm A2 .
Ti t = 0 ( chnh l O1 nhng VTCB l O2 ) 2 os 5
Asin 0
x A c
v
A2 = 5cm v ( chnh l bin tri trng vi O1)
C 20 /10
rad s T s
. n thi im 210 2
3 2,53 3 3 2
T T At T x cm
(2,5 cm l so vs gc O2 )
- Sau khi ngng tc dng F th vt li dh vi VTCB ti O1 vi bin
A1=2
2 11 2
vx
vi
1 5 2,5 7,5x cm v2 2
1 2 2 50 3( / )v A x cm s
A1
2
2 50 37,5 5 3 8,6620
cm
NX : Cu ny kh , c qua th cm thy cng c g l lm c t bt lm th , h hoy 1 lc th no li ra p n C hoc D chng hn . Th l ngi ra thnh cng khi by chng ta .
Cu 11: t in p 220 2 cos100u t (V) vo hai u on mch mc ni tip gm in tr 100R , t
in c 410
2C
F v cun cm thun c 1
L
H. Biu thc cng dng in trong on mch l
A. 2,2 2 cos 1004
i t
(A) B. 2,2cos 1004
i t
(A)
C. 2,2cos 1004
i t
(A) D. 2,2 2 cos 1004
i t
(A)
HD 100LZ ; 200CZ ; C tan 1L CZ Z
R
4
4 4i u
v 00 2,2
UI
Z
Cu 12: Gi s mt v tinh dng trong truyn thng ang ng yn so vi mt t mt cao xc nh trong mt phng Xch o Tri t; ng thng ni v tinh vi tm Tri t i qua kinh s 0. Coi Tri t nh mt qu cu, bn knh l 6370 km, khi lng l 6.1024 kg v chu k quay quanh trc ca n l 24 gi; hng s hp dn G = 6,67.10
-11 N.m
2/kg
2. Sng cc ngn (f > 30 MHz) pht t v tinh truyn thng n cc im nm trn Xch o Tri t trong khong kinh no nu di y? A. T kinh 79020 n kinh 79020T. B. T kinh 83020T n kinh 83020. C. T kinh 85020 n kinh 85020T. D. T kinh 81020 n kinh 81020T.
O1 O2
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Trn Thanh Sn H Kin Trc HN
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Cu 13: Mt ngun pht sng dao ng iu ha to ra sng trn ng tm O truyn trn mt nc vi bc sng . Hai im M v N thuc mt nc, nm trn hai phng truyn sng m cc phn t nc ang dao ng. Bit OM =
8, ON = 12 v OM vung gc vi ON. Trn on MN, s im m phn t nc dao ng ngc pha vi dao ng ca ngun O l A. 5. B. 4. C. 6. D. 7.
HD :
Cu 14: Gi M, N, I l cc im trn mt l xo nh, c treo thng ng im O c nh. Khi l xo c chiu di t nhin th OM = MN = NI = 10cm. Gn vt nh vo u di I ca l xo v kch thch vt dao ng iu ha theo phng thng ng. Trong qu trnh dao ng, t s ln lc ko ln nht v ln lc ko nh nht tc dng
ln O bng 3; l xo gin u; khong cch ln nht gia hai im M v N l 12 cm. Ly 2 = 10. Vt dao ng vi tn s l A. 2,9 Hz. B. 3,5 Hz. C. 1,7 Hz. D. 2,5 Hz.
HD:
C .
6,66OM ON
OHMN
+ S im dao ng ngc pha vi ngun trn on MH l : ( 0,5)OP k OM
6,66 ( 0,5) 8k
6,16 7,5 7k k
+ S im dao ng ngc pha vi ngun trn on HN l : ( ' 0,5 )OQ k ON
6,66 ( ' 0,5) 12k
6,16 ' 11,5k
' 7,8,9,10,11k
Vy tt c c 6 im
O
P
M
H
N
V tinh
h
00
A B
R O
HD: Mun mt v tinh trong mt phng xch o v ng yn so vi mt t, n phi chuyn ng trn xung quang Qu t cng chiu v cng
vn tc gc nh Tri t quay xung quanh trc ca n vi chu k T=24h.
Gi vn tc di ca v tinh l v , cao l h . Do chuyn ng trn nn c lc hng tm . M lc hng tm ny chnh bng lc hp dn ca tri t
C HT HDF F2
( )
mv
H R
2( )
GmM
H R
Vs 2( )v h R ; 2
T
2
2 2
.4 ( ) .
( )
m R h G M
T R h
, vi h l cao ca v tinh so vi mt t.
R + h = 42297523,87m. 35742871h m
Vng ph sng nm trong min gia hai tip tuyn k t v tinh vi tri t (phn na kia sng khng n c) T tnh c
0 '81 20R
cosR H
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Trn Thanh Sn H Kin Trc HN
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- Ta c ax 0
min 0
3mF l A
F l A
0 2l A
- MN = 10cm khi l xo khng b bin dng . Lc dao ng th M v N cch nhau xa nht = 12 cm ( tc l khi l xo dn nhiu nht ) ==> Trong on MN l xo dn 2 cm , m l xo dn u ==> v tr thp nht c l xo dn 6m
==> 0 6l A cm hay 0 0
16
2l l cm ==>
0 4l cm ==> 0
12,5
2
gf Hz
l
Cu 15: Ht nhn c ht khi cng ln th c A. nng lng lin kt cng nh . B. nng lng lin kt cng ln. C. nng lng lin kt ring cng ln. D. nng lng lin kt ring cng nh Cu 16: Khi ni v phtn, pht biu no di y ng? A. Nng lng ca phtn cng ln khi bc sng nh sng ng vi phtn cng ln. B. Phtn c th tn ti trong trng thi ng yn. C. Vi mi nh sng n sc c tn s f xc nh, cc phtn u mang nng lng nh nhau. D. Nng lng ca phtn nh sng tm nh hn nng lng ca phtn nh sng . Cu 17: Trn mt si dy n hi di 1m, hai u c nh, ang c sng dng vi 5 nt sng (k c hai u dy). Bc sng ca sng truyn trn y l A. 1m. B. 1,5m. C. 0,5m. D. 2m.
HD: 5 nt 4k . C 2
4 0,52 4
ll
(m)
Cu 18: t in p u = 220 2 cos100 t (V) vo hai u on mch mc ni tip gm in tr 20, cun cm
thun c t cm 0,8
H v t in c in dung
310
6
F. Khi in p tc thi gia hai u in tr bng 110 3 V
th in p tc thi gia hai u cun cm c ln l
A. 330V. B. 440V. C. 440 3 V. D. 330 3 V.
HD:- 80 ; 60 20 2L CZ Z Z v0
0
UI
Z =11A v tan 1 / 4
Cu 19: Hai mch dao ng in t l tng ang c dao ng in t t do. in tch ca t in trong mch dao
ng th nht v th hai ln lt l q1 v q2 vi: 2 2 17
1 24 1,3.10q q (*); q tnh bng C. thi im t, in tch
ca t in v cng dng in trong mch dao ng th nht ln lt l 10-9 C v 6 mA, cng dng in trong mch dao ng th hai c ln bng A. 4 mA. B. 10 mA. C. 8 mA. D. 6 mA.
HD : Bi ny ging dng bi c thi Cao ng C. 2012
Thay 9
1 10 ( )q C vo pt (*) 92 3.10 ( )q C
o hm 2 v ca pt (*) {Ch cng thc o hm 1( )' ( 1) . 'u u u
1 1 2 28 2 0q i q i (**) . C th m thay s vo (**)
Cch 1 :
- thi im t c Ru =110 3 .
- D dng vit c 220cos(100 / 4)Ru t
cho = 110 3
os(100 / 4) 3 / 2c t . Vit nt phng
trnh
880cos(100 3 / 4) 880sin(100 / 4)Lu t t
(*)
- Do
os(100 / 4) 3 / 2c t
sin(100 / 4) 1/ 2t
- Th vo (*) 440Lu V
Cch 2 :
Nhn thy ;R LU U vung pha nhau ,c h thc
2 2
0 0
1R L
R L
u u
U U
Tm c: - 0 0. 220RU I R V
- 0 0. 880L LU I Z V
Thay vo h thc trn 440Lu V
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Trn Thanh Sn H Kin Trc HN
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2 8i mA
Cu 20: Mt l phn ng phn hch c cng sut 200 MW. Cho rng ton b nng lng m l phn ng ny sinh ra u do s phn hch ca 235U v ng v ny ch b tiu hao bi qu trnh phn hch. Coi mi nm c 365 ngy; mi phn hch sinh ra 200 MeV; s A-v-ga-r NA=6,02.10
23 mol
-1. Khi lng 235U m l phn ng tiu th trong 3 nm l A. 461,6 kg. B. 461,6 g. C. 230,8 kg. D. 230,8 g.
HD: C E
Pt
6. 200.10 .3.365.86400E P t = 161,89216 10 ( )x J
M 26. 5,913.10
EE N E N
E
.230,8( )
A
N Am kg
N
Cu 21: Trong mt th nghim v giao thoa sng nc, hai ngun sng kt hp O1 v O2 dao ng cng pha, cng bin . Chn h ta vung gc Oxy (thuc mt nc) vi gc ta l v tr t ngun O1 cn ngun O2 nm trn trc Oy. Hai im P v Q nm trn Ox c OP = 4,5 cm v OQ = 8cm. Dch chuyn ngun O2 trn trc Oy n v
tr sao cho gc 2PO Q c gi tr ln nht th phn t nc ti P khng dao ng cn phn t nc ti Q dao ng
vi bin cc i. Bit gia P v Q khng cn cc i no khc. Trn on OP, im gn P nht m cc phn t nc dao ng vi bin cc i cch P mt on l A. 1,1 cm. B. 3,4 cm. C. 2,5 cm. D. 2,0 cm.
HD:
Cu 22: Dng mt ht c ng nng 7,7 MeV bn vo ht nhn 14
7 N ang ng yn gy ra phn ng 14 1 17
7 1 8N p O . Ht prtn bay ra theo phng vung gc vi phng bay ti ca ht . Cho khi lng cc
ht nhn: m = 4,0015u; mP = 1,0073u; mN14 = 13,9992u; mO17=16,9947u. Bit 1u = 931,5 MeV/c2. ng nng ca
ht nhn 17
8 O l
A. 2,075 MeV. B. 2,214 MeV. C. 6,145 MeV. D. 1,345 MeV.
HD:C 2( )N P OE m m m m c -1,211MeV
Li c 0PK E K K (1)
M P OP P P (Do P vung gc PP ) 0Pp p P
2 2 20PP P P (2)
T (1) v (2) ta n c ch 4,414
2,075
P
O
K MeV
K MeV
NX: Bi ny ch lng nhng ci ch lc thay khi lng cc ht nhn vo n b l nn tnh ton trng hi phc tp
Cu 23: Gii hn quang in ca mt kim loi l 0,75 m. Cng thot lectron ra khi kim loi ny bng A. 2,65.10
-19J. B. 26,5.10
-19J. C. 2,65.10
-32J. D. 26,5.10
-32J.
t gc 2PO Q v 2 1PO O
+ C tan 4,5 tan (1 tan tan ) 4,5
tan( ) 8 tan tan 8
(*)
+ T (*) 036,8 v 1 2 6OO cm
+ V bi cho Q l Cc i , P l Cc tiu nn :
2 1
2 2
2 1
2 1
2 2
2 1
36
( 0,5)
36
QO QO k
QO QO
PO PO K
PO PO
2cm ; Q thuc C k = 1
+ Gi s M l cc i thuc OP nn MinMP khi thuc C k = 2
Tnh c 1 2,5MO cm nn 2minMP cm
-
Trn Thanh Sn H Kin Trc HN
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HD: O
hcA
= 192,65.10 ( )J
Cu 24: t in p u = U0cost (U0 v khng i) vo hai u on mch mc ni tip gm in tr R, t in c in dung C, cun cm thun c t cm L thay i c. Khi L = L1 v L =L2; in p hiu dng hai u cun cm c cng gi tr; lch pha ca in p hai u on mch so vi cng dng in ln lt l 0,52 rad v 1,05 rad. Khi L = L0; in p hiu dng gia hai u cun cm t cc i; lch pha ca in p hai u
on mch so vi cng dng in l . Gi tr ca gn gi tr no nht sau y? A. 1,57 rad. B. 0,83 rad. C. 0,26 rad. D. 0,41 rad.
HD: ng vi cc iu kin ca bi ta c cng thc
1 21 2 ax ax2 0,785( )
2M M rad
Cu 25: Tia no sau y khng phi l tia phng x?
A. Tia . B. Tia +. C. Tia . D. Tia X. Cu 26: Cc mc nng lng ca cc trng thi dng ca nguyn t hir c xc nh bng biu thc
2
13,6nE
n (eV) (n = 1, 2, 3,). Nu nguyn t hir hp th mt phtn c nng lng 2,55 eV th bc sng
nh nht ca bc x m nguyn t hir c th pht ra l A. 1,46.10
-8 m. B. 1,22.10
-8 m. C. 4,87.10
-8m. D. 9,74.10
-8m.
HD:Ban u mt cng vit 1 ng biu thc tnh 1 2 3 4, , , ,...E E E E Sau ngi m mm th thy 4 2 2,55E E eV .
Nguyn t t trng thi dng n = 2 hp th nng lng ri nhy ln 4 . 41MIN
4 141
hcE E
8
41 9,74.10 (m)
NX : Bi ny c th nhm MIN 42
Cu 27: Mt sng hnh sin ang truyn trn mt si dy theo chiu dng ca trc Ox. Hnh v m t hnh dng ca si dy ti thi im t1 (ng nt t) v t2 = t1 + 0,3 (s) (ng lin nt). Ti thi im t2, vn tc ca im N trn y l A. 65,4 cm/s. B. -65,4 cm/s. C. -39,3 cm/s. D. 39,3 cm/s.
HD: T hnh v nhn thy 40cm 15
50( / )0,3
v cm s ( da vo 2 nh sng nh ln cao , chng cch nhau 3
khong =15cm v lch nhau 0,3s )40
0,8( )50
T s
Thy N VTCB AX 39,3( / )N Mv v A cm s . Do sng ang truyn theo chiu dng nn N phi i ln
Cu 28: t vo hai u cun s cp ca my bin p M1 mt in p xoay chiu c gi tr hiu dng 200V. Khi ni hai u cun s cp ca my bin p M2 vo hai u cun th cp ca M1 th in p hiu dng hai u cun th cp ca M2 h bng 12,5 V. Khi ni hai u cun th cp ca M2 vi hai u cun th cp ca M1 th in p hiu dng hai u cun s cp ca M2 h bng 50 V. B qua mi hao ph. M1 c t s gia s vng dy cun s cp v s vng dy cun th cp bng A. 6. B. 15. C. 8. D. 4.
HD: Gi s vng dy s cp, th cp ln lt ca my 1: 1N v 2N
Gi s vng dy s cp, th cp ln lt ca my 1: 1N v 2N
+ C 1 1
2 2
U N
U N 1
2 2
200 N
U N (1)
+ Lc u 2 1 2 1
2 2 2
' '
' ' 12,5 '
U N U N
U N N (2)
+ Lc sau 2 2 2 2
2 1 1
' '
' ' 50 '
U N U N
U N N (3)
Ly (2) x (3) 2
221 25
50.12,5
UU V . Ri thay vo (1) : 1
2
2008
25
N
N
-
Trn Thanh Sn H Kin Trc HN
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u 29: Mt khung dy dn phng, dt, hnh ch nht c din tch 60 cm2, quay u quanh mt trc i xng (thuc mt phng ca khung) trong t trng u c vect cm ng t vung gc vi trc quay v c ln 0,4 T. T thng cc i qua khung dy l A. 2,4.10
-3 Wb. B. 1,2.10
-3Wb. C. 4,8.10
-3Wb. D. 0,6.10
-3Wb.
HD : 4 30,4.60.10 2,4.10BS Wb
Cu 30: in nng c truyn t ni pht n mt khu dn c bng ng dy mt pha vi hiu sut truyn ti l 90%. Coi hao ph in nng ch do ta nhit trn ng dy v khng vt qu 20%. Nu cng sut s dng in ca khu dn c ny tng 20% v gi nguyn in p ni pht th hiu sut truyn ti in nng trn chnh ng dy l A. 85,8%. B. 87,7%. C. 89,2%. D. 92,8%.
HD:
2 2cos
PRP Px
U ; trong t x l
2 2cos
R
U ==>
PPx
P
C 11
0,1P
PxP
(1) v 2
2
PP x
P
2 11,2t tP P ==> 2 2 1 11,2( )P P P P ==>
2
2 2 1 11,2( 0,1 )P P x P P ==>1
2
2
1 1,08P
P xP
==> 121 2
0,11
PP
P P
t 1
2
Pk
P ==>
0,11 1,08k
k ==>
1 0,812k ==>2
2 2 2
2
0,123 1 1 87,7%P
P x H P xP
Cn vi 2 2 20,114 0,877 12,3%k P x H
Cu 31: Bit bn knh Bo l r0 = 5,3.10-11m. Bn knh qu o dng M trong nguyn t hir bng
A. 84,8.10-11
m B.21,2.10-11
m. C. 132,5.10-11
m. D. 47,7.10-11
m.
HD:2.n Or n r =
10 114,77.10 47,7.10m m
Cu 32: Hai con lc n c chiu di ln lt l 81 cm v 64 cm c treo trn mt cn phng. Khi cc vt nh ca hai con lc ang v tr cn bng, ng thi truyn cho chng cc vn tc cng hng sao cho hai con lc dao
ng iu ha vi cng bin gc, trong hai mt phng song song vi nhau. Gi t l khong thi gian ngn nht
k t lc truyn vn tc n lc hai dy treo song song nhau. Gi tr t gn gi tr no nht sau y? A. 8,12s. B. 2,36s. C. 7,20s. D. 0,45s
.HD : 1 2
1 2
;0,9 0,8
g g
l l
. Vit Phng trnh
1
2
cos0,9 2
cos0,8 2
x A t
x A t
(Vit x hay u c v con lc dao ng iu ha )
Sau cho 1 2x x ; ri gii tm c 2 nghim
2
0,9 0,8
2
0,9 0,8
kt
kt
Thay k vi cc gi tr sao cho t >0 th thy MINt =0,423
-
Trn Thanh Sn H Kin Trc HN
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CH : Bi ny hi ging kiu bi con lc trng phng nhng khng phi vy , iu kin bi con lc trng
phng l
1 2
1 2
1 2
, 0
, 0
x x
v v
v v
tc l phi cng li v cng chiu chuyn ng . Cn bi ny th ch cn cng li
Cu 33: Mt vt nh dao ng iu ha theo phng trnh x = A cos4t (t tnh bng s). Tnh t t=0, khong thi gian ngn nht gia tc ca vt c ln bng mt na ln gia tc cc i l A. 0,083s. B. 0,125s. C. 0,104s. D. 0,167s.
HD : Cho AX / 2Ma a / 2x A .
t = 0 l VTCB n / 2x A mt / 6Mint T 0,083 Cu 34: Hai dao ng u ha cng phng, cng tn s c bin ln lt l A1 =8cm, A2 =15cm v lch pha
nhau 2
. Dao ng tng hp ca hai dao ng ny c bin bng
A. 7 cm. B. 11 cm. C. 17 cm. D. 23 cm.
HD: V hnh v thy A l cnh huyn Tam Gic Vung 2 21 2A A A
Cu 35: Gi l nng lng ca phtn nh sng ; L l nng lng ca phtn nh sng lc; V l nng lng
ca phtn nh sng vng. Sp xp no sau y ng?
A. > V > L B. L > > V C. V > L > D. L > V >
Cu 36: Hin nay urani t nhin cha hai ng v phng x 235 U v 238 U , vi t l s ht 235 U v s ht 238 U l
7
1000. Bit chu k bn r ca 235 U v 238 U ln lt l 7,00.108 nm v 4,50.109 nm. Cch y bao nhiu nm,
urani t nhin c t l s ht 235 U v s ht 238 U l 3
100?
A. 2,74 t nm. B. 2,22 t nm. C. 1,74 t nm. D. 3,15 t nm. HD: Gi ci thi im cch y bao nhiu nm l thi im ban u
0235
0238
3
100
N
N . V ci thi im hin ti l thi gian n b phn r
235 0235
238 0238
N N
N N 1 2
1 1ln 2. ( )
et
T T
Gii v tm c t=1,74 t nm
Cu 37: Trn mt ng thng c nh trong mi trng ng hng, khng hp th v phn x m, mt my thu cch ngun m mt khong d thu c m c mc cng m l L; khi dch chuyn my thu ra xa ngun m thm 9 m th mc cng m thu c l L 20 (dB). Khong cch d l A. 8 m B. 1 m C. 9 m D. 10 m
HD : C AL L v ' 20AL L db
M '9
20logA Ad
L Ld
. T y 1d m
Cu 38: Trong chn khng, nh sng c bc sng ln nht trong s cc nh sng n sc: , vng lam, tm l A. nh sng tm B. nh sng C. nh sng vng. D. nh sng lam. Cu 39: on mch ni tip gm cun cm thun, on mch X v t in (hnh v). Khi t vo hai u A, B in
p AB 0u U cos( t ) (V) (U0, v khng i) th:
2LC 1 , ANU 25 2V v MBU 50 2V , ng thi
ANu sm pha 3
so vi
MBu . Gi tr ca U0 l
A. 25 14V B. 25 7V C. 12,5 14V D. 12,5 7V
HD :
-
Trn Thanh Sn H Kin Trc HN
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+ C : AN AM X
MB X NB
u u u
u u u
, m
2 1 L CLC U U hay 0L C L Cu u u u
==> 2AN MB X Yu u u u ==> AN MB YU U U
Cu 40: Mt vt nh khi lng 100g dao ng iu ha vi chu k 0,2 s v c nng l 0,18 J (mc th nng ti v
tr cn bng); ly 2 10 . Ti li 3 2 cm, t s ng nng v th nng l A. 3 B. 4 C. 2 D.1
HD: C 2 21
2E m A 6A cm . C 3 2x cm
2 2v A x 10 18
2
2 2
W1D
T
v
W x
II.PHN RING A.Theo chng trnh chun Cu 41 : Khi ni v quang ph vch pht x, pht biu no sau y l sai? A. Quang ph vch pht x ca mt nguyn t l mt h thng nhng vch sng ring l, ngn cch nhau bi nhng khong ti. B. Quang ph vch pht x do cht rn hoc cht lng pht ra khi b nung nng. C. Trong quang ph vch pht x ca nguyn t hir, vng nh sng nhn thy c bn vch c trng l vch , vch lam, vch chm v vch tm. D. Quang ph vch pht x ca cc nguyn t ho hc khc nhau th khc nhau. Cu 42: Mt mch LC l tng ang thc hin dao ng in t t do. Bit in tch cc i ca t in l q0 v cng dng in cc i trong mch l I0. Ti thi im cng dng in trong mch bng 0.5I0 th in tch ca t in c ln l:
A. 0q 2
2 B. 0
q 5
2 C. 0
q
2 D. 0
q 3
2
HD : Dng h thc lin h
2 2
0 0
1q i
q I
Cu 43: Cho khi lng ca ht prtn, ntrn v ht nhn teri 21D ln lt l 1,0073u; 1,0087u v 2,0136u. Bit
1u= 2931,5MeV/c . Nng lng lin kt ca ht nhn 2
1D l:
A. 2,24 MeV B. 4,48 MeV C. 1,12 MeV D. 3,06 MeV
HD: 21 (2 1)P n DE m m m c Cu 44: Mt vt nh dao ng iu ha vi bin 4cm v chu k 2s. Qung ng vt i c trong 4s l: A. 8 cm B. 16 cm C. 64 cm D.32 cm
HD: 4 2s T S=8A
Cu 45: Mt con lc n c chiu di 121cm, dao ng iu ha ti ni c gia tc trng trng g. Ly 2 10 . Chu k dao ng ca con lc l:
Do 2MB ANU U v ANu lch MBu l 3
, ta c gin vc t
+ 25 6PQ 25 6
2PI
+ 2 2: 12,5 14OPI OI OP PI
==> AB L X Cu u u u ==> 12AB XU U
==> 0 12,5 14. 2 25 7ABU (V)
-
Trn Thanh Sn H Kin Trc HN
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A. 1s B. 0,5s C. 2,2s D. 2s
Cu 46: Gi s mt ngun sng ch pht ra nh sng n sc c tn s 7,5.1014Hz. Cng sut pht x ca ngun l 10W. S phtn m ngun sng pht ra trong mt giy xp x bng: A. 0,33.10
20 B. 2,01.10
19 C. 0,33.10
19 D. 2,01.10
20
HD : 1t s E = N. =N.hfE
Nhf
=192,01.10
Cu 47: t in p u=U0cos 100 t12
(V) vo hai u on mch mc ni tip gm in tr, cun cm v t
in c cng dng in qua mch l i=I0 cos 100 t12
(A). H s cng sut ca on mch bng:
A. 1,00 B. 0,87 C. 0,71 D. 0,50
HD : 3
cos 0,876 2
Cu 48: Thc hin th nghim Y - ng v giao thoa vi nh sng n sc c bc sng . Khong cch gia hai khe hp l 1mm. Trn mn quan st, ti im M cch vn trung tm 4,2mm c vn sng bc 5. Gi c nh cc iu kin khc, di chuyn dn mn quan st dc theo ng thng vung gc vi mt phng cha hai khe ra xa cho n
khi vn giao thoa ti M chuyn thnh vn ti ln th hai th khong dch mn l 0,6 m. Bc sng bng A. 0,6 m B. 0,5 m C. 0,4 m D. 0,7 m
HD: Lc u M l vn sng 5 nn 5MD
xa
(1)
Lc sau di chuyn mn th M c 2 ln tr thnh vn ti ti v n chnh l vn ti th 4 . Cc bn v hnh ra s thy ( Ban u M l sng 5 ri dch mn sang phi 1 cht s b ti ln 1 v s ng vs vn ti th 5 , li dch tip sang phi th n li b ti ln 2 v s ng vi vn ti th 4 ) . My ci vn sng ti ny n b loe to dn ra ging hyperbol ca giao thoa sng
( 0,6)
3,5MD
xa
(2) . Gii (1) v (2) 1,4D m . Ri thay
D vo (1) hoc (2) bit 4,2Mx mm s suy ra 0,6 m Cu 49: Trong mt th nghim v giao thoa sng nc, hai ngun sng kt hp dao ng cng pha ti hai im A v B cch nhau 16cm. Sng truyn trn mt nc vi bc sng 3cm. Trn on AB, s im m ti phn t nc dao ng vi bin cc i l A. 10 B. 11 C. 12 D. 9
HD: 0 0AB k AB
Cu 50: t in p xoay chiu u=U 2 cos t (V) vo hai u mt in tr thun R=110 th cng dng in qua in tr c gi tr hiu dng bng 2A. Gi tr ca U bng
A. 220V B. 220 2 V C. 110V D.110 2 V
HD: .U I R
Ghi Ch : Bi lm c s tham kho ca mt s cc thy c trn thuvienvatly.com ; dethi.violet.vn
Nhn chung thi L nhng nm gn y c kh dn theo thi gian , nm nay cu d th rt d cn nhng cu kh th cng tot m hi , ngi nh gii gy bt kho cng khng ra K thi 2013 kt thc , chc nhng bn s t khi c c li gii v nhng dng ch ny c nhng ngi mm ci , c nhng ngi ci tht to ,tht ln v ch my chc na chng ta s c mt ngi trng mi , nhng ngi bn mi , nim vui mi do chnh chng ta la chn . Hy cm nhn mt thi sinh vin p m khng phi ai cng c c hi c n Thn gi cc bn