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Serbian physics Olympiad from 2014.
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7. J 2012/2013.
j , j j
18-19. 5. 2013.
1: (10 )
j j j 19. j. j j j . (). j , j j j . j .
j m = 57 g, j a oj j D ( 1)j I = 0,057 kg m2. j, j j j .
o
D
31 cm 36 cm
d
1:
() j jj . D, j o. o , j . j j d D ( 1). v , d, I m. j j j j , j j j. j, j j . (1,5 )
() - j . j j j d D (1). D, j o. j j e j . e j I, m
1: 1 3
7. J 2012/2013.
j , j j
18-19. 5. 2013.
d. j j j j , j j j. j, j j . (1,5 )
j ( 2), . j . J- , , . j j S j. j .
2: - 3:
() , ( ) . . j j j j F = RN , j R j , N j -. j j j , N a ( 3). j 3, F j , j jF R, j R . a j R, R, m M . j a j R = 32,5 mm, R = 0,05,m = 57 g M = 180 g. j j j IL =
2
3mR2. (2 )
1: 2 3
7. J 2012/2013.
j , j j
18-19. 5. 2013.
() j , j - j j . j j j j j j e =
v2yV2yv1y
, v1y v2y j y -
, V2y j y ( S). j 2. j j eP =
v2yv1y
. eP j e,
m M . j eP j e = 0,9, M m j j (). (1 )
() 1 = 450 v1 = 30
m
s(
S, 2). j 1 = 300rad
s
j 2. N j j j (). 2 j S . j 2 S. j m,M , R, R, eP a . () (), eP = 0,40 a = 3,0 mm. j S , ? (4 )
: , ,
: J, ; , ,
j : , ,
1: 3 3
7. J 2012/2013.
j , j j
18-19. 5. 2013.
2: (10 ) a j j - j - . j , , j. j - j 1880. , , , , (, ).
1:
j -j j j j - . J jj j j (1), j je a - j, , , , - j.
A: - (4 )
j . -, S m, - j (2). j - , j n . j k. j - , j j X0.
2: J
.1. U . , j - j X1. Fq U X0, X1, S, k n.
.2. , j j x j, U . x X0, X1, k,n, m x, j j 0 X0, X1, k, n m.
.3. j L -. j j j X1, j j j x. j j j x q . x q X1, S, k, n, m, L, U , x q.
2: 1 3
7. J 2012/2013.
j , j j
18-19. 5. 2013.
.4. j j, x = 2x q = 2q. -j X0, X1, S, k, n, m L. j j j j X0 X1 j ?
: (1,5 )
- j - . e j - , - j j j b = 7,83 106 kg/s. j , j j (a 3). j j , j , - . j -j . j j j j .
3: K
, -, j. x j j j j - j j j ( j j x). j j- :
x+ x+ 20x = f0 cos(t+ ).
j . e j m = 0,243qV , je - q = 2659 kg/m
3, V j j . -
j j k = EWD3
4L3, j J E =
7,87 1010 N/m2, W = 0,127mm, D = 0,325mm L = 2,809mm j .
.1. a j j - m, k, x, b F = F0 cos(t+ ).
.2. j 0.
.3. j e x = x0 cos(t + ). x0 j = f0, , 0.
2: 2 3
7. J 2012/2013.
j , j j
18-19. 5. 2013.
: (3 )
q j j j x, j - = 8,13 106 C/m. j , j. q j x, j j - Re, j Le Ce.
.1. j , - j j e.
.2. j .
.3. Re, Le Ce - j .
.4. e - , - . j .
: j (1,5 )
E j j - . 4 j , j a je f = 215 Hz.
.1. jj - j ?
.2. j - - ?
.3. j j -.
.4. jj , j - j jj 25 oC, -j jj 10 oC?
4: j
: , ,
: , ,
j : , ,
2: 3 3
7. 2012/2013.
18-19.5.2013. ,
3: (10 )
, , 31,1mV = . 0 0,187kgm = .
o1 20 Ct = 5
0 1,013 10 Pap = . 31 1,2kg/m= .
) 2t ? (2) ) o3 110 Ct = .
. . (2) ) ( ). o3 110 Ct =
o20 C 50 1,013 10 Pap = . h ? (2) ) h ( ) 10mh = . . (4) 29,81m/sg = .
* * * * * * * * * *
0
0
0( ) gx
px e
= , 0 0p 0x = . axe , a 1ax : 1axe ax .
: , , : . , , : , ,
7. J 2012/2013.
j , j j
18-19. 5. 2013.
1:
() j 12I2 = 1
2mv2 + 1
2I21, j 1
. jj o D I = mvd+ I1. j v =
2IdI+md2
.
j d =
Im
= 1 m. j d = 1 m j , j. d = 67 cm. j , j. d = 31 cm.
() j 12mv2 = 1
2mv21 +
12I2, j v1
. jj o - D mvd = I mv1d. j j j e =
v1v.
j e = Imd2
I+md2. j e(d)
d 0 d =
Im
= 1 m. j ,
j (d = 67 cm), j (d = 31 cm).
() j jmdvxdt
= F M dVxdt
= F ,
a j ILddt
= FRNa. j vx R =
Vx, j.dvxdt Rd
dt= dVx
dt. j F = RN . j
a = RR(
53
+ 2m3M
)= 3,05 mm.
() y mv1y = MV2y +mv2y. -j e eP eP =
eMmM+m
= 0,443.
() S j: 1) j ; 2) , . j j IL
ddt
= FR
mdvydt
= N , j t1 -
t2 j m (v2y v1y) = t2t1Ndt IL (2 1) = R
t2t1Fdt,
2 t2. v2y = eP v1y F = SN , j j- j 2 = 1
3v1 sin 12R
S (1 + eP ). j -
j m (v0x v1x) = t0t1Fdt, IL (0 1) =
t0t1FRdt
MV0x = t0t1Fdt, j t0 j , -
0 j . v0x + R0 = V0x j
t0t1Fdt = v1 cos 1+R11
M+ 5
2m
, j
0 < 0. j ( j F j () j 0 < 0) jj j IL (2 1) =
t0t1FRdt
t2t0FRdt+
t2t0Nadt
m (v2y v1y) = t0t1Ndt+
t2t0Ndt. j
j j F = SN , j F = RN , j
7. J 2012/2013.
j , j j
18-19. 5. 2013.
2 = 11+
v1 cos 1R
5
3+ 2m
3M
(1 + eP )v1 sin 1
R32
(R
aR
)+ 1
S
(R
aR
)1+
v1 cos 1R
5
3+ 2m
3M
. j-
2 j 1) 2) j j
grS =
v1 cos 1+R1(1+eP )v1 sin 1(mM +
5
2)
= 0,359, S < grS
, S > grS . -
j 2 S j . S = grS
j j .
0 0.2 0.4 0.6 0.8S
-300
-200
-100
0
100
200
300
2[rad/s]
1: 2 S
7. J 2012/2013.
j , j j
18-19. 5. 2013.
2:
A: -
A.1. (0,5 ) j j j , mg = nk(X X0), j X . , j - j mg + Fq = nk(X X1), j Fq = nk(X0X1). j - j q0 =
0SX1U . j Ep j j .
j, , 2SEp =q00. j j
j j Fq = q0Ep =q20
20S= 0SU
2
2X21
= nk(X0X1), j
U = X1
2nk(X0X1)
0S.
A.2. (0,5 ) j X1 + x , -
j j j F q =0SU2
2(X1+x)2
0SU2
2X21
0SU2
X31
x = Fq 0SU2
X31
x,
j F e = nk(X X1x). mx = F e mg F
q (nk
0SU2
X31
)x = nk(3 2X0X1)x. , j
j j 0 =
nkm(3 2X0
X1). j
j 3X1 > 2X0.
A.3. (2 ) U = Lq + (q0+q)(X1+x)0S
, j
q0 =0SUX1
.
j qx, j q = ULX1
x X1L0S
q.
j Fq =q20
20S. j F q =
(q0+q)2
20S
q20
20S+ q0
0Sq, j F e = nk(XX1x).
x = nkmx U
mX1q.
A.4. (1 ) j x = 2x q = 2q j .3. j: (2 X1
L0S)q U
LX1x = 0 (2 nk
m)x U
mX1q = 0. j
j j (2 X1L0S
)(2 nkm) = U
2
mLX21
= 2nk(X0X1)mL0S
.
21 =nkm 22 =
X1L0S
, j jj:
4 2(21 + 22) +
21
22(3 2X0/X1) = 0. j
= 12
[21 +
22
41 +
42 2
21
22(5 4X0/X1)
]1/2,
j j, j 3X1 > 2X0.
:
.1. (0,2 ) J j jmx+bx+kx = F0 cos(t+).
.2. (0,3 ) j j .1. m j j - j j , j -
j = bm= b
0,243 qWLD= 104 s1 0 =
km=
ED2
0,972 qL4= 2,27 105 rad
s.
7. J 2012/2013.
j , j j
18-19. 5. 2013.
.3. (1 ) x = x0 cos(t+) j x+x+20x = f0 cos(t+ ),
j = f0 = F0/m, j 2x0 cos(t + ) x0 sin(t + ) +
20x0 cos(t+ ) = f0 cos(t+ ) cos + f0 sin(t+ ) sin . j sin(t + ) cos(t + ) j j x0(
2 20) = f0 cos
x0 = f0 sin , j x0 =f0
(220)2+22
= arctg 22
0
.
:
.1. (1 ) j j j P = xV0. j j , P = 2F0x. jV0 = 2F0.
.2. (0,6 ) j , j j m
q + b
q + k
q = F0 cos(t + ) =
2V0 cos(t+ ).
.3. (0,7 ) j Leq + Req + q/Ce = V0 cos(t + ),
j Le =2m2
= 2,27 kH, Re =2b2
= 237 k, Ce =2
2k= 8,54 fF.
.4. (0,7 ) j ReLeCe j - C j . j 1.
1:
: j
.1. (0,1 ) j j ff
= 0, t0 = 25
C.
.2. (0,1 ) j ff
= TT
< 0, .
.3. (0,8 ) j j , j t0 = 25
C , j ff
= (t t0)2, j j
j . j , . (70 106,10 C),j = 7010
6
2025 C2= 3,5 108 C2. , j -
j f(t) = (1 3,5 108(t/C 25)2) 215Hz.
.4. (0,5 ) , - T . f
f= T
T T = f
fT = 3,5 108(10 25)2
365 24 60min 4,14min, .
7. 2012/2013.
18-19.5.2013. ,
3: ) : 2 0 1 Vg m g Vg+ = (0,5), 2 2t . : 0 1 2( )m V= (0,2). 1T 2T , : 1 1 /p RT M= (0,5) 2 2 /p RT M= (0,5). : 12
0
1
1
TTm
V
=
(0,2). 2 341KT =
o2 68 Ct = (0,1).
) 3 383KT = , 3 0gF Vg m g= + (0,5). : [ ]1 1 3 0( )T gF Vg F V m g = = (0,3). ) : 1 3 3 1 / /T T= (0,6), : 11 0
3
(1 )TTF V m gT
=
(0,5). 1,2NTF = (0,1).
) h : 3 0 hVg Vg m g= + (0,7) : 3 0 /h m V= + (0,3).
h : 1
0
1
gxp
h e
= (0,4).
h : 0 01 111 1
0 13
ln ln 843m
h
p p Vh Tg gm V
T
= =
+ (0,6).
) h h+ : 1 1
0 0
( )
1
g h h g hp p
h h he e
+
+ = = (1). , 31
0
10 1
g hp
, 1
0
(1 )h h h
g hp+
(0,5). : 2
10 3 0 3
0
( ) ( ) hh h
gm V a m V g Vg V h k h
p++ = + + = (1,5).
:
0 3 0 3 0 02
h 1 1
( ) 22 2 186s
m V m V p pTk g V g+ +
= = = = (1).
7. 2012/2013.
- 1 4
18-19. 5. 2013.
,
(20 ):
(LEDLight Emitting Diode) . , LED , .
LED. (photodiodePD). , ( , W/m2).
: 1) PD . 2) LED . 3) LED, . LED.
. , LED p-n . LED, p-n , :
: - - -
LED ( ), LED.
LED :
LED LED ( LED). LED .
. . e, a , . .
( ) ( )
.
7. 2012/2013.
- 2 4
:
1. ,
2. , 3. , 4. , 5.
LED ,
6. ,
7. , . , DCV V , ( ).
a , X Y . LED X , Y ( 1). . 2. LED . LED .
1. .
2. .
7. 2012/2013.
- 3 4
: LED .
:
(1) LED , . LED.
(2) ( Y-) LED. LED
. LED . . .
(3) LED , . LED.
(4) .
1. (5 )
1.1 LED ( ). LED . LED LED X-, .
( ) . , LED . 10 . . (2 )
1.2 1.1 . (3 )
2. LED (5 )
2.1 ( ) LED.
LED . . ( ) . LED . LED . LED .
LED . 20 0-2 V 5 2-6 V . . (3 )
2.2 LED LED . . (2 )
7. 2012/2013.
- 4 4
3. LED (10 )
3.1 ( ) y- , LED
. LED. LED , .
. ( ) . . (3 )
3.2 3.1. (
/ ) LED . (7 )
:
. . LED . . . . R1 ( 100 k).
. .
: , , : , , , , : , ,
7. 2012/2013.
- 1 6
18-19. 5. 2013.
,
1.1 LED
( ) .
(
) ( ) LED :
(1)
x (mm)
(mV) (mV) (A)
-1/2 (A
-1/2)
0 981 113 8,68 339
30 591 180 4,11 493
60 446 215 2,31 658
90 379 220 1,59 793
120 325 240 0,85 1085
150 309 243 0,66 1231
180 304 250 0,54 1361
210 286 244 0,42 1543
240 276 240 0,36 1667
270 266 237 0,29 1857
300 260 236 0,24 2041
1.2 LED . ,
LED LED
:
( )
(2)
x , d , LED . LED:
( )
(3)
:
(4)
-1/2
x, , .
7. 2012/2013.
- 2 6
0 50 100 150 200 250 300
500
1000
1500
2000I P
D (A
-1/2
)
x (mm)
2.1 LED
( ) . R3 (
) (
) LED :
(5)
(mV) (V)
(mV)
(mV) (mA) (mW) ( A)
/ (mA/W)
23 1,662 148 144 0,0767 0,127 0,04 0,3139
100 1,711 176 153 0,333 0,570 0,23 0,4033
151 1,725 179 143 0,503 0,868 0,36 0,4146
201 1,735 202 153 0,67 1,16 0,49 0,4215
254 1,744 223 159 0,847 1,48 0,64 0,4334
313 1,751 240 160 1,04 1,83 0,8 0,4379
408 1,762 270 162 1,36 2,4 1,08 0,4507
517 1,771 303 165 1,72 3,05 1,38 0,4522
603 1,777 334 171 2,01 3,57 1,63 0,4564
709 1,784 372 177 2,36 4,22 1,95 0,4625
807 1,79 398 176 2,69 4,82 2,22 0,4610
915 1,796 433 179 3,05 5,48 2,54 0,4639
1023 1,802 468 180 3,41 6,14 2,88 0,4687
1116 1,806 492 179 3,72 6,72 3,13 0,4659
1196 1,809 518 183 3,99 7,21 3,35 0,4645
1322 1,815 552 180 4,41 8,0 3,72 0,4651
1425 1,819 583 181 4,75 8,64 4,02 0,4653
7. 2012/2013.
- 3 6
1526 1,822 614 179 5,09 9,27 4,35 0,4694
1632 1,827 646 182 5,44 9,94 4,64 0,4669
1693 1,828 668 184 5,64 10,32 4,84 0,4692
1807 1,832 698 180 6,02 11,03 5,18 0,4694
1904 1,835 733 187 6,35 11,65 5,46 0,4688
1990 1,838 765 192 6,63 12,19 5,73 0,4699
2660 1,857 962 190 8,87 16,47 7,72 0,4689
3010 1,866 1063 187 10,03 18,72 8,76 0,4679
3430 1,876 1179 179 11,43 21,45 10,0 0,4662
4160 1,892 1401 182 13,87 26,24 12,19 0,4646
4580 1,9 1518 177 15,27 29,01 13,41 0,4623
5220 1,911 1694 177 17,4 33,25 15,17 0,4562
5840 1,922 1876 178 19,47 37,41 16,98 0,4538
6270 1,93 1996 176 20,9 40,34 18,2 0,4512
2.2 LED . :
(6)
. LED
(7)
(8)
LED
LED 5 mA.
7. 2012/2013.
- 4 6
0 5 10 15 20
0.30
0.35
0.40
0.45
I PD/P
LED
(mA/W
)
ILED
(mA)
3.1 LED, ILED LED
, . ( ) ri , . , . LED .
R3 (
) ( ) LED
( ):
(9)
(mm) ( ) (mV)
( ) (mV) ( ) ( A)
( ) ( Am)
0 561 140 4,21 0
1 522 136 3,86 3,86
2 476 133 3,43 6,86
3 443 127 3,16 9,48
4 394 119 2,75 11,0
5 333 115 2,18 10,9
6 279 111 1,68 10,08
7 234 99 1,35 9,45
8 206 93 1,13 9,04
9 186 88 0,98 8,82
10 159 83 0,76 7,6
7. 2012/2013.
- 5 6
11 131 79 0,52 5,72
12 109 75 0,34 4,08
13 100 72 0,28 3,64
14 89 68 0,21 2,94
15 83 66 0,17 2,55
16 79 65 0,14 2,24
17 74 61 0,13 2,21
18 71 59 0,12 2,16
19 68 57 0,11 2,09
20 67 57 0,10 2,00
21 66 57 0,09 1,89
0 5 10 15 20
0
1
2
3
4
I PD (A)
ri(mm)
3.2 , LED . a .
7. 2012/2013.
- 6 6
LED . ( , ). i- . , , LED, :
( ) ( ) ( ) (10)
je ( ) , ( ) , q .
:
( ) ( ) (11)
:
( ) ( )
(12)
o , i- :
( ) ( )
(13)
LED je:
( ) =
( )
(14)
( )
(15)
LED
(16)
LED. LED, , . (15), LED je
( ) . (16) .