đề thi học sinh giỏi lý lớp 9

so'c;rAo DVC va nao
I}EN TRI'

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rao
Dn 1'IIr HQC SINr{ GIOI LOp 9 TnUNG r_roc
'co so NAnn IrQC 2ol3 Mdn: VgT L,i
Thli gian: 150 phrit (kh6ng ke ph6t dA)

-

2ot4

I (4 ctid@: I-Iai guong phing Gl vd G2 dugc bo tri sau cho m{t phan xp cta

chring quay vdo nhau vd hqp v6i ,hau mQt g6c a nhu hinh vc.
MQt &6m sang s
duo. c dflt vdo khoing gifia hai guong
a) Trinh bdy cdch y.c du_d'ne di cria tia s6ng xu6t ph6t ru s d6n guong G1, ph6n
xa trcn G1 rdi dcn g[p gusng G2 ph6n xp tr6n gu$rg G2 viruu-do cho tia
phin x4 sau ctrng di qua S.
b) Bitit
1990, ctrtng t6 g6c hsp boi ria tdi ban dAu vd tia phan xp
ra kh6i
!
guong G2 khdng phu thugc vio g6c tdi mi chi phu thugc
veo g6c'ho. p b0i
hai guong.

"

c:a:?^(4

lusng kd bang nh6m c6 khOi lusng m (ke) 0 nhiqt dQ t1
lIQt
lide:
: 23'c, cho
vdo nhiet rugng k6 mOt ttroi luqng m (kg) nu6c b nhiet ao tr. sau khi
hQ can
nhiQt d[ ctu nudc giam d"i /C.iiilr*; ;d iffi";#;dte;
?-:e
Lhi:t,
luons
nhiQt

k:.7:
chAt l6ng khac (Ehang fic dyng h6a hpc vdi nu6c) d nhiQt
Ifgl
d0 ts = 45"c, khi c6 can b6ng nhiQt l6n hai, nhiQt dQ cria nu6c trong
nhiQt fuqng k6
lai giAm 100C so vdi.nhiQt OO.1n Uing nirigt iAntfr,i nr,it. Tim nhiQt dung ri6ng
cria ch6t long.d6 AO tnem vdo nhiQt t"irg f.A Uigt ,frigt dung ri6ng cria
nh6m vd
cua nu6c ldn lugr ld c1 900 J/kg.Ki cz= 42A0 tkg.K. 86 qru,UIt
uo dai nhiQt
vdi rndi trulng bOn ngoii.

lot

:

c:r 1fi-!i6y):H*ai v,ar crryyel d0ng da_u1r€n cirng mQt duong thing. N6u chfng

chuy€n dQng lpi g6n

nhau thi c* sau l phrit khoin[ cacn gim"chrhng-gia* di 330
Ndu chring chuy6n d01g cung chi6u
icilng *ui* jlrat vd vdn di vdi
,'i,
1;
ld'n nhu cil.) thi ctsau- 10 gi6y thi khoing rarn gina chring
"a,
l4i ting ir,e,, zs m.
Tinh vgn t6c cfia rndi vat.

iilo


Cfru 4

:

ft

ctiA@: Cho mqch diQn nhu hinh vE, bitit Uou 12 V, R1
R: 1 Q; bo qua diQn trd ciic dopn ddy n0i vA ctia c6c kh6a K.
a) I(1, I(2 diru rncy. Tinh hiQu diOn ih6 b) Kr d6ng,.I(2 m&. Tinh cudng dQ dong di6n qua R2.
c) I(1, K2 d6r"r d6ng. Tfnh cuong dQ ddng di6n qua K1 vdr K2.

:

:

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:

ft4

:2 f), R2 :

:

CAu 5
ctiint): Cho mpch diQn nhu hinh v6, UiSt U :24 y, lfo 4 e, Rz i5 fJ;
ddn D ld lopi ddn tr0n b6ng c6 ghi 6 V - 3 W vd s6ng binh thuong. Vdn k6 c6 di-€n
ho vd cung l6n vd.chi 3 v, chot duong c,ria von k6 mic vdo di0m M, b6 qua diQn
trl cilc dopn d0y nOi. finn R1 vd R3.

-Hot-


so c;rAo DUc vA DAo TAo
I}IIN TI{E

HrloNG oAN cuavr
=TIII HQC SINI{ CT6r
LO} 9 TRUNG

DE

HQC CO SO CAr,

NIm hgc 2013 -2014
M6n thi: VAT LY

riXU

N6i dun

g
guong Gr ld Sr, Sr Id var cira Gz qua G2 cho anh
Y? Tm gtu Oya
d€ tia sdng sau khi phdn x4 tr€n Gz cho tia ph6n xa qua Ai6m
S ta
,r6if?.u^"i S.f1o'1e ndy cit G,ztqi J.(ld diOmtdi trCn guong c).
Noi sr vdi J duongnity c*tcr tdi I (le dicm t6i trEn gu"crng G1).Sau
d6 ta ndi hai diOm S, I ta rO tiu tqi g+p guong C1.
YQy tia s6ng xu6t ph6t tu s d6ni
*a trcn G1 d6n G2 tpi J cho
rlt
tia phAn x4 qua S.
b)

:)

SV,

.

*

1,50d


Tir gi6c OINJ c6 I: J : 90'(IN vd JN li ph6p tuy

*

0+N=1g00<+g+N:1g00

t4i I vd J)
(1)
(2)

N+i + j: 1800
Xdttamgi6c INJ co:
TiI (1) vd (2)
=) g: i + j
MA B le g6c ngoii cita tam gi6c ASIJ n6n B : 2(i + j) :2cr (di6u phAi

2,5.0 d

chirng minh)

I{ri

c6 cdn bing nhiet lAn thri nh6t, nhiqt d0 cdn bdng cua hQ lA t, thi:
(1)
m.cr(t-tr)
:
mir t tz- 9 ; cr 900 J/kg.K, cz: 4200 J/kg.K. (2)

900(tz -9 -23):4200(tz-t2 +9)
Tt (1) va
tz - 32) 42
900(tz - 32) = 4200.9
=
65oC
suy ra: tz: J4oC

: m.c2(t2-t)

:

(2)

*

; t:

I(hi c6 cAn b[ng

:

)

nhiQt lAn thrl hai, nhiQt dO cdn

2,00 d

bing cria hQ ld t', thi:

(3)
2m.c1(t' - tg) : (mc1+ mc2xt- t')
(4)
t':t- 10=65 - 10:55; tl:450C
md
:
+2c(55 - 45) (900 + 4200)(6s - ss)
Tir (3) ve (a)

+

g

2c.10: 5100.i0

2,00 d

s = 2.550'J/kg.K

Ggi sr vir sz ld qgdng dudng chuyi5n dQng cria m5i vat; v1 vi v2 |i vfn
t6c cua m6i vat. Gi6 sri vr ( vz)
Ta c6: sr

:60vr

(1)

sz:60v2 Q)

lai gAn nhau, khoAng c6ch cira hai vpt giim

(3)
beng t6ng qudng dudng hai v$t da di. sr * sz:330 m
+ v2):330 * v1 * Y2:5.,5
Y2:5,5 - (4)
60(v1+
60(v1
Tir (1), (2), (3) tac6:
cuahai vft
khoang
c6ch
chi6unhau,
ctng
Khi hai vft chuy6n dQng
(5)
tdng bing hiQu qu6ng ducrng hai vflt dA di.
-t, =25 m

I(hi hai v4t chuyAn

dQng

rnfltkh6c:

",

s,

= 10.vr

sz=to.vz

(6),(7)tac6: .10(v2-vr):25 >Yz-'tt:2,5
Ley @) + (8) v0 theo vO ta dugc: 2v2:8
)\2 :4 m/s

Tu(5),

:)y1

:1,5m/s

d
1, )u
50 o
|| l,
I

(6)

I

O

I

I

(8) | t, SOa
I
I

lf.OOA


a) I(ri I(r vd K2 citng md 4 di6n trd mdc n6i ti6p:
Ras :6 f)
r-r

l-ll-

'-

Uno
Ruo

HiQu diqn tli6 hai dAu

-n

^

Rz: Uz:

I.Rz

:2Y

1,00d

b) I(hi I(r d6ng, K2 mo doan AC bi n6i tit Uec: 0,

c)

ddng diQn kh6ng Qua R2 hay 12:0
Klri Kr vd I(z cilng d6ng, tac6:Rr//P.z//(R3nt R4)
ddng diOn Qua K1t IKt 12 * I3a

0,50d

:
y-rn= utn :9=4A
Rr+& 3

1r:um
'Rzl =9=l2A
=) ls:12
:
dong diQn Qua K2: Irz Ic - Is+
Utn
1.:
" Rnu= +=22
li

A.

+

4:

16

1,50d

A

(vi Ras =

*t,

:? trrz:ZT-4:18A

1,00d

Ro

N
Do diQn trd cria v6n k6 v6 cirng l6n

nOn

ta c6 m4ch diQn dugc mic nhu

sau:
[(R1 nt

ta c6:

Iz =

I:vd

hiQu diQri th6 trdn R:

ta c6:

Pta)/ (Rznt R3)] nt Rs
11

li:

:

tr=

5A
*-- *=0,

UNe: Iz.Rr

UMs: Uo:6 V

1,00d


-

=

(=l*I2.R3
3:12.R3*r^- 3

md

3
I:I1 *I2:0,r*&

I

|

-)lz:&

|

...
(1)

I

I 1,00

d

I

m[t lih6c:

U: LRo + I2(R2 + R3)

I

I

tray

=)

24:(o,s+|1.+*]frs+R3)
R3'

&'

(2)

D:!=R::3f)
&

thay (2) vdo

(1)

=+ I

=

1, 5

|
I

lr,OOO

A

_'l

IJae

:

U-I.Ro =24

-

1,5.4

:

18

V

Ut:Uee-ljd:18- 6:l2Y
R,' =

4 =12 =24 f)
It

0,5

1,00 d