Giải chi tiết đề thi thử THPT quốc gia môn lý 2015 lần 2

Câu Lạc Bộ Yêu Vật Lý
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Câu 1: B
Câu 2: C
Câu 3: D
Câu 4: D
Câu 5: B
Câu 6: B
Câu 7: B
Câu 8: B
Câu 9: A
Câu 10: A
Câu 11: A
Câu 12: A
Câu 13: D
Câu 14: D
Câu 15: C
Câu 16: B
Câu 17: C
Câu 18: C

Câu 19: A
Câu 20: A,D
Câu 21: A
Câu 22: B
Câu 23: A
Câu 24: D
Câu 25: B
Câu 26: D
Câu 27: D
Câu 28: A
Câu 29: A
Câu 30: D
Câu 31: B
Câu 32: A
Câu 33: C
Câu 34: B
Câu 35: D
Câu 36: B
Câu 37: B
Câu 38: C
Câu 39: B
Câu 40: B
Câu 41: A
Câu 42: D
Câu 43: A
Câu 44: D
Câu 45: C
Câu 46: B
Câu 47: B
Câu 48: D

Câu 49: B
Câu 50: B
Câu 1: D i 
Câu 2: L bii gian, li suy ra chn C
Câu 3: Mt vu, t s gi  (  thu h
0). Khi t ng gim mt na so v s  
A.
δ
4
B.
δ
16
C.
δ
4δ+1
D.
δ
3δ+4

Lời giải: [Hinta]
1
1
1
44
4
1
4 4 4 4 4
1
44
34

W W W W . W
W
WW
W
. W.
W
d t d
d
dd
tsau


 






    




       









V
Câu 5:  bii ta th  vi khoa hai
ngn s va chm gia thuyu cp bn s 
t t ca thuy truyT truyng
A. 7,5m/s.
B. 2,5m/s.
C. 2,0m/s.
D. 4,0m/s.
Lời giải : [Hà Dũng]
ng kiu 2 vc chiu gc 

 








 








 






V
Câu 7: a v  u khic.  
Câu 8: Thay thng s thy B sai.


Câu Lạc Bộ Yêu Vật Lý
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Câu 9: Mn t truyn t m n v ng
Bc.  mt th m ng t 
Bit  ng cm ng t cm ng t 
l
A. xung; 0,06 T.
B. 
C. 
D. xung; 0,075 T.
Lời giải: [Hinta]
ng quy tc nm i, suy ra t ng xu 

4
0 06
0 15 10
, ( )
,
x
xT  
. V
Câu 11: Cho mn t u, hin th cu bn t 
0
. Ti thm
hiu n th u bn t gin so vi hin th  ch bng kI
0
, vi
I
0
 i trong m c
B. 99,4%
A. 99,7%
C. 92,3%
D. 96,1%
Lời giải: [Hà Dũng]





 







 













Hay 


V
Câu 15: u
u = U 2cos(ωt + φ)
u mn mch gn tr R mc ni tip vi
mt cun cm thun L, bin tr  gp 3 ln ci u
R

L
lc thi  u

n tr  u cun cm thun L  t thm. H th
A.
2 2 2
RL
90u +10u = 9U
. B.
2 2 2
RL
45u +5u = 9U
. C.
2 2 2
RL
5u +45u = 9U
. D.
2 2 2
RL
10u +90u = 9U
.
Lời giải: [Hinta]
 
22
0 0 0 0
2 2 2 2
2 2 2 2 2 2 2 2 2
0 0 0
2 2 2 2
0 0 0 0
2 2 2
3 3 10
99

1 1 9 9 9 9 2
9 10 5
5 45 9


.
L R L L
R L R L
R L L R L R L
R L L L
RL
R Z U U U U
u u u u
u u U u u U u u U U U
U U U U
u u U
     
               
  


Câu 16: Cho phn ng h
2
He
3
+
0
n
1
t ca h

2
He
3
. Bi ht khi
cng ngh ct c phn ng nhing ngh ct
sau phn 
2
= 931 (MeV).
A. 7,7187 (MeV).
B. 7,7188 (MeV).
C. 7,7189 (MeV).
D. 7,7186 (MeV).
Lời giải : [Hà Dũng]
E=3,25=



 






 => 


V
Câu 17: Chic x n s f
1

c tc x. Chi
hydro bc x n s f
2
c tc x. Bi hydro cho bi biu thc
E
n
=
0
2
E
-
n
(vi E
0
ng s  s tn s ca hai bc x 
A.
1
2
f
3
f 10

.
B.
1
2
f
10
f3


.
C.
1
2
f
25
f 27

.
D.
1
2
f
128
f 135

.
Lời giải: [Hinta]
 3 bc x  c x  n=5
 T s tn s hai bc x 
2
2
1
1
25
3
1
27
1
5




.
V


Câu Lạc Bộ Yêu Vật Lý
_____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
_____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________




Câu 20: n mch AB gm hai hc ni tip, trong mi hp ch cha mt linh kin thuc lon
tr thun, cuc t u n mch AB m
2
cos2ft (V) vi
u chnh tn s  f
0
u dng giu h
X

Y

= 100
3
u t ca m s t cn mn s 
tr f
0


A.
12
3
B.
2
1

C.
1
2
D.
3
2

Lời giải: [Hinta]


 
 
2
2 2 2 2 2
2
2 2 2 2 2 2
100 3 100 200
2 100
AB Y
NhËn xÐt ta thÊy:
VËy chøng tá u vu«ng pha víi u . Sau khi t¨ng f th× tÇn sè m¹ch t¨ng,
vËy hép Y chÝnh l¯ cuén d©y v¯ hép X l¯ tô ®iÖn

YX
R L C R L L C C
U U U
U U U U U U U U U U
   
        
   
22
3 400 100 3 0
150 50 3 200
3
2
( ) ( ) v¯ ( )
VËy dÔ d¯ng cã cos
L
L R C
U
U v U v U v

  
    


Câu 21: m Y- ng thi 2 bc x c
m

64,0
1

)


m

48,0
2

n gi
  
A. 
B. 
C. 
D. 
Lời giải: [Hinta]

1
2
0 64 4
0 48 3
,
,



.
Suy ra trong khop gi 
Vn gi 
Câu 22: H
1
1
A

Z
X
 
2
2
A
Z
Y
bn. Coi khng hai hng s khi ca
 u mu
1
1
A
Z
X
t. Bia
1
1
A
Z
X
 thm
t
1
 s khng ca
1
1
A
Z
X


2
2
A
Z
Y

1
2
A
7A
n thm t
2
 s kh
A.
1
2
7A
8A
.
B.
1
2
A
31A
.
C.
1
2
A

32A
.
D.
1
2
A
14A
.
Lời giải : [Hà Dũng]




































 



 
 

  

.
i 

:

































V

Câu 24: Chiu bc x n s t kim lo n. Gi s mt
p th  dng mt phi bi
Nu tn s ca bc x chiu t
A. 4K + A
B. 2K
C. 4K
D. 4K + 3A.
Lời giải: [Hinta]
43
4
W
W
W
d
dsau
dsau
hf A
KA
hf A


  



. V


Cõu Lc B Yờu Vt Lý
_____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

_____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________




Cõu 26: n mch RLC ni tip, cuthun cm. Khi ni tt t n
u dng gin tr n trong hai trung hi nhau. H s
sun mng:
A.
5
1
. B.
5
2
. C.
10
1
. D.
10
3
.
Li gii: [Hinta]
c hn d nh
H s t:
13
3
10
cos arctank

. V
Cõu 27: t n u n mch AB ni tip gn tr thun R, t n
cm thu t cc. Khi ch L = L
0
u du cun cm
U
L
t c
Lmax
U
. Khi L = L
1
hoc L = L
2

L1
= U
L2
= 0,9
Lmax
U
. H s t ca mch AB khi
L = L
1

2
bng 1,44. H s t cn mch AB khi L = L
0

bng
A, 0,5 B, 0,6 C, 0,7 D, 0,8
Li gii: [Hinta]


0
10
1 2 0
12
0 9 1
22
1 44 3
max
Ta có công thức tính nhanh: U cos
Vậy từ bi toán ta có: cos , ( )
Mặt khác 2 giá trị của L cho cùng một U nên ta có công thức: ( )
Bi toán cho ta biết: cos cos , ( )
Từ (
LL
L
U

2 0 1
10
1 0 0
0 1 0
1 0 1
2
09
0 9 0 8
2 1 44
2 1 44
cos ,
1),(2) v (3) ta có: cos , cos ,
cos .cos ,
cos cos ,

V
Cỏch khỏc: Li gii ca Admin Kai Shi

R
ZCosU
ZZRR
ZRU
ZcZR
ZU
U
L
CL
L
L
L
L

)(

)(
.
2222

=.>
R
UCos
Z
U
L
L



=.
max2121
2.
)
11
(
L
L
LL
L
L
L
L
L

Z
U
ZZ
U
Z
U
Z
U



R
CosU
Z
U
CosCos
R
U
L
L 0
max
max:
21
8.1.8.1
)(

8.0
8.1
21
0





CosCos
Cos
=> ỏp ỏn D
Cõu 28: u s dng cho chi c 208 lm/W
i nhi nh quang tu
nh quang v s tin phi tr cho phn ching
dng b
s dng ch chii mt kic khong bao nn cho vic
chi L gn nht.
A. bng.
B. ng.
C. mt tring.
D. ng.
Li gii: [Hinta]


Câu Lạc Bộ Yêu Vật Lý
_____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
_____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

100
57 7 120 57 7 62 3
208 120
12 747 6
, , ,
.,
x
x k k k k
k
       
  

 
Câu 29: n mch xoay chiu AB gm R = 30, cu , L =
0,3
π
 n dung C
c mc ni tip theo th t n th xoay chiu u = 100
2
cos100i ta thy
rng khi C = C
m
n th hiu dng  n mch cha cu n (U
1
t cc titr
ca C
m


1min

A.
-3
10
3π

B.
-3
10
π

C.
-3
10
3π

2
V.
D.
-3
10
π

2
V.
Lời giải: [Hinta]
 
   
 

2
2
2 2 2
2
2
2
2
2
1
30
25
2
1
.
min
min ( )
LC
LrC
LC
LC
LrC L C C
LrC
U r Z Z
U
U
R Rr
R r Z Z
r Z Z
U Z Z Z
U

Uv
R Rr
r



  


     




V
Câu 30: Cho phn ch ca Urani:
1 235 95 139 1
0 92 42 57 0
27n U Mo La n e

    
. Bit khng h
U

= 234,99 u; m
Mo
= 94,88 u; m
La
= 138,87 u; m
n

t to nhit c
6
J/kg. Khi
  to 
A. 1616 kg
B. 1717 kg
C. 1818 kg
D. 1919 kg
Lời giải: [Hà Dũng]
E =



 

 

 

 


 MeV = 3,4473.


1g 





 => 







ng c




Vy kh





. 
Câu 31: Cho mn gm ba phn t mc ni tip theo th t n c t cm
n tr thu R = 100

 n
mu tn s i ta thy khi L = L
1

2
=
1

L
2

th n mch b n tc thi lch pha nhau m ca L
1
n
dung C l
A.
4
2 3 10
H; F.
33



B.
4
4 3 10
H; F.
33



C.
4
1 3.10
H; F.
4
3




D.
4
4 3 3.10
H; F.
23




Lời giải: [Hinta] Cách giải tổng quát cho mọi bài toán liên quan đế độ lệch pha của dòng điện, có thể hơi dài!!!
i, tng tr ng hng nhau.
t
21
2  
LL
Z x Z x

12
2 1,5      
C C C
Z Z x Z Z x Z x
.(1)
Khi L=L
1

1
2
tan




C
xZ
R
. Khi L=L
2

2
tan



C
Zx
R

 ng hp l
2 /3


12
2 /3
  


 
12
12

12
tan tan
tan tan(2 /3) 3
1 tan tan

  


     




Câu Lạc Bộ Yêu Vật Lý
_____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
_____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________




x (cm)
t (10
-1
s)
x
1
x
2
22
3. 1 .

   

    


C C C C
x Z Z x x Z Z x
R R R R
(2)
Kt h
1
400 3
0 5 0 5 0 5 0 5 0 5
3 1 3 200 3
300 3
, , , , ,
.
L
C
Z
x x x x x
x
R R R R R
Z




        








V
Câu 32: Bn ht  y ra phn ng tt ht ht proton.
Bit rng hai hn tn ng 1,21 (MeV). Cho khng c
h
O
m

= 0,21(m
O
+ m
p
)
2

p
m

= 0,012(m
O
+ m
p
)
2
. t  

A. 1,555 MeV.
B. 1,656 MeV.
C. 1,958 MeV.
D. 2,559 MeV.
Lời giải: [Hà Dũng]
ng bng :














 






 

















 























=>



























L : 

 

 











 




V
Câu 33:  x
1

2

 th . Tng t cng  
mt th ln nh



A. 
B. 
C. 
D. 
Lời giải: [Hinta]
Ti th ving ca tng v
 
12
8 2 6 2
2
cos , cosxx

  

   


. Vy hai v tng hp bng 10cm/s

 
200
Max
/v A cm s



.
Vy 
Câu 36: Hai v m c
v       ng ca hai v 
1
2
8 3cos( )( )
2
x t cm
T



2
2
8cos( )( )x t cm
T



. Khong thi gian ngn nht k t khi khoa hai vng
nh nhn khi khoa hai vt ln nh K t thu, th
vt ci l
A. 1,5s.
B. 1s.
C. 0,5s.
D. 0,25s.
Lời giải: [Hinta]
a hai v
12

8 8 16
23
d x x


       

Khong thi gian ngn nht k t khi khoa hai vng nh nhn khi kho
gia hai vt ln nh
Tht ci l
11
1
4 12
. ( )t T s

  





Câu Lạc Bộ Yêu Vật Lý
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V
Câu 37: a con lu vt  t nh

ca con l v 
1
n v 
2
vi t bi ng ci trung
m cn x
1
x
2
  v 
1
n v 
2

A. 1 cm/s.
B. 2 cm/s.
C. 3 cm/s.
D. 4 cm/s.
Lời giải: [Hinta]
 
 
22
1 2 1 2 1 2 1 2
1 2 1 2 1 2
11
100 100 100
22
1
100 50 100 2 2
2

WW
( / )
tt
t k x x t k x x x x t
S
k x x x x t x x t S t cm s
t
        

          



V
Câu 38: ng  x
1
= 4cos( + 
1
)  x
2
= 4cos( + 
2
) cm.
Bit 0  
2
 
1
  ng tng hp c x = 4cos( + ) cm. Khi x = - 2

A. x

1
= 0 m.
B. x
1
= 2 cm 
C. x
2
= 2 cm 
D. x
2
=  4 cm.
Lời giải: [Hinta]
0  
2
 
1
  vy vt 2 s
1
=A
2
=A=4cm. V lch pha gia hai v
0
.
Khi x = -  ng tng h -120
0
suy ra v -60
0
.
Kt lun: V x
2

= 2 cm .
V
Câu 39: u con lc
ng ch ca tr 
0
. Khi con l 
0
ng m

ca con l 
A. Gim 25%.
B. 
C
D. Gim 50%.
Lời giải: [ Hà Dũng]
22
0
00
2
2 2 2 2
0
0 0 0
33
1
2 2 4 4 2
3 2 3 5
2
2 4 2 2 4 4 2 8
Tríc khi chÞu t¸c dông cña ®iÖn trêng:
( ) Khi = th× W

qE
Khi chÞu t¸c dông ®iÖn trêng: g'=g+ =2g
m
'
' ' ( )
Tõ (1) v¯ (
d
td
mgl mgl
WW
mg l mgl mgl mgl
W W W mgl

  

   

   

      
5
1 25 0 25
4
'
2) , ' ,
W
WWW
W
       

V
Câu 40: c gm 7 np lu quãng tám 
bit b s do
1
, do
2
T s tn s ca hai nt quãng tám 
3
2
()
2
()
f do
f do

).
Khoa hai nt nhc trong mt quãng tám ng cung nửa cung. Mi quãng tám c chia
 gmột cung nửa cung :


Hai nt nhnửa cung ng vi hai nt nh s tn s 
12
2
(VD:
12
()
2
()
f do
f si


).
Bit rla
3
n s 440Hz, tn s cdo
1

A. 40 Hz.
B. 65 Hz.
C. 80 Hz.
D. 95 Hz.
do
rê
mi
fa
sol
la
si
do
1
1
1/2
1
1
1
1/2


Câu Lạc Bộ Yêu Vật Lý
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Lời giải : [Hà Dũng]







y 



n n






















. V
Câu 41: Cho mt con lng . Li ci c
rng vt gia tc a = g/2 l
1
= 9 N 
2
= 5 N. Cho bi
 vng h ng ca con l
li ci cng
A. 10 N.
B. 14 N.
C. 7 N.
D. 4 N.
Lời giải : [Gs Xoăn]

Câu 42: Cho mt con lng. Mt hc sinh ting. Ln th nht,
i th nh i gian ngn nht vn v i trin th t v v 
n dng ri th nh i gian ngn nhc phc hi chi s
x2
y3


. T s gia
tc vc trng ngay khi th ln th nh
A. 0,8.
B. 1,5.
C. 12.
D. 2.
Lời giải: [Hinta]
m t:




m:




 m  c tic l n nhau v th 
ng h n v ng hp kia.
 m 2: Vn v n dang ri th nh t v 
kn d  t dao ng t  VTCB suy ra t
2
=T/4 suy ra t
1
=T/6.
 
1
=T/6. Ti gian v n v n d
/3. Khi vt  v n d




.
 ng   /cos/3) =



.
Gia tc ca vt khi th vt (c ca vt  v 

A)
Suy ra a = 2g.Hay a/g =.
V
Câu 43: Ti mn xoay chiu mn th hiu
dng  hai cc ci. Ni hai cc ci mt tr s 
t t i cung c
t ho s k =  n
hong ch  n th 
pha v n. Do xy ra s c  i ta ni trc tiic ca
 


Câu Lạc Bộ Yêu Vật Lý
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A. 

B. 
C. 
D. 
Lời giải: [Gs Xoăn]

Câu 44: t s ng ti N
pha vng ti M. Bi ti b
A. 4 cm, 40 cm.
B. 4 cm, 60 cm.
C. 8 cm, 40 cm.
D. 8 cm, 60 cm.
Lời giải: [Hinta]
 ng tng t t
ng hp duy nhnh N.
2 2 20 10 60
66
. ( )MN NP cm


      
.

2 12
NP


 ti N bng 1 n ti bng
V
Câu 45: Giống i xì đề đại học.
Câu 46: Mt ngui, truyu mng.

B qua s hp th  ngu
 ng
A
L
= 30
dB

B
L
= 60
dB.
i O hai ngun ging ngut
ng th n nht
ma x
L
c gần giá trị
nào nhất 
A. 70
dB.

B. 65
dB.

C. 77
dB.

D. 71
dB.

Lời giải : [Hà Dũng]



 




=30 => 


 m cng cao h t O xung












. T c OH=0,9995 OB
T c 

 








 







 
V
Câu 47: Cho mn AB gm mn tr thun R mc ni tip vi mt t n C vt cu
t. Gm ni gin tr thun v m ni gia t n vn
mp xoay chi hiu dng 120
3
i, tn s f = 50 Hz u dng
gi
AN
lch pha
2

so v
MB
ng thi u
AB
lch pha
3


so vi u
AN
.
Bit ti ca mu ni tu cut ti ca mch bng
A. 810 W.
B. 540 W.
C. 240 W.
D. 180 W.
Lời giải: [Hinta]
Nhc chn cun tr trong r.
t chun thy u
AN

MB
 pha vi u
AN
. Chn pha ca u
AN
0. 


Câu Lạc Bộ Yêu Vật Lý
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 

0
26
23
u cos ,u =120 cos ,u =120 cos
AN AN MB AB
U t t t

  
   
  
   
   


6 2 169 7
3 2 6
120 120 ,
AB AM MB R MB R AB MB
u u u u u u u u
  
           
.
V n th u mch lch nhau 30
0
.
360 120 3 2
6
cos . .cos ( )
AB
P U I I I A



     
.
60R  
.
Vt mch khi ni tt cu
 
 
2
2
22
120 3
0 540
60 6
.cos cos (W)
AB
AN R
U
P
R



    


.
V
Câu 49: u n n mch AB mc ni ti). Bit t 


C
, cun cm thu
L

2

= 1.  th biu din s ph thui gian ca 
gin mn mu dng gim A

A. 50
7
V.
B. 25
14
V.
C. 25
7
V.
D. 12,5
14
V.

Lời giải: [Hinta]
Nhc c
T d ki
L
, u
C


0
L C L C L C
Z Z u u u u      


L

C
 tri
AB X
uu
.
T c
x
i quyt xong  
a!!!
Ta ving ti thm 2/3 ct l:
 
2
200 100
3
cos ; cos
AN MB
u t u t

  

   



L
 
2
200 100
7
3
50 7
2 2 9
AN C X
AN MB
X
MB L X
u u u
uu
u
u u u




    






    







7 50 7
50 7 25 14
9
2
()
AB X hieudungAB
u u U v


     


.
V
Hết
ng ti hc 2015 ch a. B gng tranh th i gii cho
n tham khc vt nhiu thi ng h 
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