WBJEE Physics & Chemistry (Descriptive) - Previous Year Paper, 2011

# WBJEE Physics & Chemistry (Descriptive) - Previous Year Paper, 2011 | WBJEE Sample Papers, Section Wise & Full Mock Tests 2024 PDF Download

``` Page 1

WBJEE - 2011 (Hints & Solutions) Physics & Chemistry

1. A shell of mass m is at rest initially. It explodes into three fragments having masses in the ratio 2 : 2 : 1. the fragments having
equal masses fly off along mutually perpendicular direction with speed V. What will be the speed of the third (lighter) fragment?
A.
From conservation of momentum
1
O2mv 2 mv =+
V
1
= 22v -
Hence, velocity of third part is 22v at an angle of 135
o
with either part.
2. A small spherical ball of mass m slides without friction from the top of a hemisphere of radius R. A T what height will the ball lose
contact with surface of the sphere ?
A. If the ball lose contact at B then, from conservation of energy.
mg cos?
mg sin?
R
R cos = h ?
R - R cos ?
N
mV
2
R
A
V
()
2
1
mgR 1 cos mv
2
-?=
v
2
= 2gR (1 – cos?) ......(i)
At B
2
mV
N mg cos
R
+= ?
When the ball will lose the contact
N = O
2
mv
mg cos
R
?=
DESCRIPTIVE TYPE QUESTIONS
SUB : PHYSICS & CHEMISTRY
Page 2

WBJEE - 2011 (Hints & Solutions) Physics & Chemistry

1. A shell of mass m is at rest initially. It explodes into three fragments having masses in the ratio 2 : 2 : 1. the fragments having
equal masses fly off along mutually perpendicular direction with speed V. What will be the speed of the third (lighter) fragment?
A.
From conservation of momentum
1
O2mv 2 mv =+
V
1
= 22v -
Hence, velocity of third part is 22v at an angle of 135
o
with either part.
2. A small spherical ball of mass m slides without friction from the top of a hemisphere of radius R. A T what height will the ball lose
contact with surface of the sphere ?
A. If the ball lose contact at B then, from conservation of energy.
mg cos?
mg sin?
R
R cos = h ?
R - R cos ?
N
mV
2
R
A
V
()
2
1
mgR 1 cos mv
2
-?=
v
2
= 2gR (1 – cos?) ......(i)
At B
2
mV
N mg cos
R
+= ?
When the ball will lose the contact
N = O
2
mv
mg cos
R
?=
DESCRIPTIVE TYPE QUESTIONS
SUB : PHYSICS & CHEMISTRY
WBJEE - 2011 (Hints & Solutions) Physics & Chemistry

V
2
= gR cos ? ........(ii)
? from (i) & (ii)
2Rg(1 - cos ) = gRcos ??
2 – 2 cos ? = cos ?.
2 = 3 cos ?.
? Height from the ground
h = R cos ? =
2R
3
3. Two identical cylindrical vessels, with their bases at the same level, each cotain a liquid of density p. The height of liquid in one
vessel in h
1
and that in the other is h
2
. The area of either base is A. What is the work done by gravity in equalizing the levels
when the vessles are interconnected ?
A.
P
h
1
A A h
2
?
Let find height = h
12
hh
h
2
+ ??
?=
??
??
decerese in height
12 1 2
1
hh h h
hh
22
+- ??? ?
?= - =
??? ?
??? ?
Mass of liquid
( )
12
hh
mA
2
-
=?
? Work done
12 12
hh hh
WA
22
?- ? - ?? ? ?
=?
?? ?? ??
?? ? ? ??
=
()
2
12
hh
gA
4
-
?
4. A battery of emf E and internal resistance r is connected across a pure resistive device (such as an electric heater) of resistance
R. Prove that the power output of the device will be maximum if R = r.
A. I
R
r
E
E
I
Rr
=
+
Page 3

WBJEE - 2011 (Hints & Solutions) Physics & Chemistry

1. A shell of mass m is at rest initially. It explodes into three fragments having masses in the ratio 2 : 2 : 1. the fragments having
equal masses fly off along mutually perpendicular direction with speed V. What will be the speed of the third (lighter) fragment?
A.
From conservation of momentum
1
O2mv 2 mv =+
V
1
= 22v -
Hence, velocity of third part is 22v at an angle of 135
o
with either part.
2. A small spherical ball of mass m slides without friction from the top of a hemisphere of radius R. A T what height will the ball lose
contact with surface of the sphere ?
A. If the ball lose contact at B then, from conservation of energy.
mg cos?
mg sin?
R
R cos = h ?
R - R cos ?
N
mV
2
R
A
V
()
2
1
mgR 1 cos mv
2
-?=
v
2
= 2gR (1 – cos?) ......(i)
At B
2
mV
N mg cos
R
+= ?
When the ball will lose the contact
N = O
2
mv
mg cos
R
?=
DESCRIPTIVE TYPE QUESTIONS
SUB : PHYSICS & CHEMISTRY
WBJEE - 2011 (Hints & Solutions) Physics & Chemistry

V
2
= gR cos ? ........(ii)
? from (i) & (ii)
2Rg(1 - cos ) = gRcos ??
2 – 2 cos ? = cos ?.
2 = 3 cos ?.
? Height from the ground
h = R cos ? =
2R
3
3. Two identical cylindrical vessels, with their bases at the same level, each cotain a liquid of density p. The height of liquid in one
vessel in h
1
and that in the other is h
2
. The area of either base is A. What is the work done by gravity in equalizing the levels
when the vessles are interconnected ?
A.
P
h
1
A A h
2
?
Let find height = h
12
hh
h
2
+ ??
?=
??
??
decerese in height
12 1 2
1
hh h h
hh
22
+- ??? ?
?= - =
??? ?
??? ?
Mass of liquid
( )
12
hh
mA
2
-
=?
? Work done
12 12
hh hh
WA
22
?- ? - ?? ? ?
=?
?? ?? ??
?? ? ? ??
=
()
2
12
hh
gA
4
-
?
4. A battery of emf E and internal resistance r is connected across a pure resistive device (such as an electric heater) of resistance
R. Prove that the power output of the device will be maximum if R = r.
A. I
R
r
E
E
I
Rr
=
+
WBJEE - 2011 (Hints & Solutions) Physics & Chemistry

Power  P = I
2
R =
()
2
2
ER
Rr +
For maximum power
dp
0
dR
=
() ()
()
2
2
Rr .1 R.2Rr
E0
Rr4
??
+- +
= ??
+
??
??
R + r – 2R = 0
r = R
5. A radioactive isotope X with half life 1.5 × 10
9
yrs. decays into a stable nucleus Y . A rock sample contains both elements X and
Y in ratio 1 : 15. Find the age of the rock.
A.
X Y
t = 0, 16 0
t = 1, 1 15
9
1
2
T 1.5 10 yr =×
n
o
1
NN
2
??
=
??
??
1 = 16
n
1
2
??
??
??
n4
11
n4
22
?? ? ?
=?=
?? ? ?
?? ? ?
? time t = 4 × 1.5 × 10
9
= 6 ×10
9
yrs
6. The bacterial growth follows the rate l aw,
dN
KN
dt
=
where ‘K’ is a constant and ‘N’ is the number of bacteria cell at any time.
If the population of bacteria (no. of cell) is doubled in 5 minutes, find the time by which the population will be eight times of the
initial one.
A.
dN
KN
dt
=
(1st order kinetics)
? N = N
0
e
kt
(integrating)
? in 5 min, N = 2N
0
0
2.303 N
Klog
tN
=
Page 4

WBJEE - 2011 (Hints & Solutions) Physics & Chemistry

1. A shell of mass m is at rest initially. It explodes into three fragments having masses in the ratio 2 : 2 : 1. the fragments having
equal masses fly off along mutually perpendicular direction with speed V. What will be the speed of the third (lighter) fragment?
A.
From conservation of momentum
1
O2mv 2 mv =+
V
1
= 22v -
Hence, velocity of third part is 22v at an angle of 135
o
with either part.
2. A small spherical ball of mass m slides without friction from the top of a hemisphere of radius R. A T what height will the ball lose
contact with surface of the sphere ?
A. If the ball lose contact at B then, from conservation of energy.
mg cos?
mg sin?
R
R cos = h ?
R - R cos ?
N
mV
2
R
A
V
()
2
1
mgR 1 cos mv
2
-?=
v
2
= 2gR (1 – cos?) ......(i)
At B
2
mV
N mg cos
R
+= ?
When the ball will lose the contact
N = O
2
mv
mg cos
R
?=
DESCRIPTIVE TYPE QUESTIONS
SUB : PHYSICS & CHEMISTRY
WBJEE - 2011 (Hints & Solutions) Physics & Chemistry

V
2
= gR cos ? ........(ii)
? from (i) & (ii)
2Rg(1 - cos ) = gRcos ??
2 – 2 cos ? = cos ?.
2 = 3 cos ?.
? Height from the ground
h = R cos ? =
2R
3
3. Two identical cylindrical vessels, with their bases at the same level, each cotain a liquid of density p. The height of liquid in one
vessel in h
1
and that in the other is h
2
. The area of either base is A. What is the work done by gravity in equalizing the levels
when the vessles are interconnected ?
A.
P
h
1
A A h
2
?
Let find height = h
12
hh
h
2
+ ??
?=
??
??
decerese in height
12 1 2
1
hh h h
hh
22
+- ??? ?
?= - =
??? ?
??? ?
Mass of liquid
( )
12
hh
mA
2
-
=?
? Work done
12 12
hh hh
WA
22
?- ? - ?? ? ?
=?
?? ?? ??
?? ? ? ??
=
()
2
12
hh
gA
4
-
?
4. A battery of emf E and internal resistance r is connected across a pure resistive device (such as an electric heater) of resistance
R. Prove that the power output of the device will be maximum if R = r.
A. I
R
r
E
E
I
Rr
=
+
WBJEE - 2011 (Hints & Solutions) Physics & Chemistry

Power  P = I
2
R =
()
2
2
ER
Rr +
For maximum power
dp
0
dR
=
() ()
()
2
2
Rr .1 R.2Rr
E0
Rr4
??
+- +
= ??
+
??
??
R + r – 2R = 0
r = R
5. A radioactive isotope X with half life 1.5 × 10
9
yrs. decays into a stable nucleus Y . A rock sample contains both elements X and
Y in ratio 1 : 15. Find the age of the rock.
A.
X Y
t = 0, 16 0
t = 1, 1 15
9
1
2
T 1.5 10 yr =×
n
o
1
NN
2
??
=
??
??
1 = 16
n
1
2
??
??
??
n4
11
n4
22
?? ? ?
=?=
?? ? ?
?? ? ?
? time t = 4 × 1.5 × 10
9
= 6 ×10
9
yrs
6. The bacterial growth follows the rate l aw,
dN
KN
dt
=
where ‘K’ is a constant and ‘N’ is the number of bacteria cell at any time.
If the population of bacteria (no. of cell) is doubled in 5 minutes, find the time by which the population will be eight times of the
initial one.
A.
dN
KN
dt
=
(1st order kinetics)
? N = N
0
e
kt
(integrating)
? in 5 min, N = 2N
0
0
2.303 N
Klog
tN
=
WBJEE - 2011 (Hints & Solutions) Physics & Chemistry

?
o
0
2N 2.303
Klog
5N
??
=
??
??
min
–1

?
2.303
Klog2
5
=
for 8N
0

o
o
8N 2.303
tlog
2.303
N
log 2
5
??
??
=
??
??
??
??

?
53log2
t15min
log 2
×
==
? time required is 15 min.
7. In ‘x’ ml 0.3 (N) HCl, addition of 200 ml distilled water or addition of 100 ml 0.1 (N) NaOH, gives same final acid strength.
Determine ‘x’.
A. When 200 ml H
2
O is added to x ml solution
(x) (0.3) = (x + 200) (Y) ? final conc.
Y =
0.3x
200 x +
in 2nd case
Number of equivalents of  HCl after NaOH addition
0.3x
0.01
1000
-
( no of eq. of NaOH added = 0.01)
? conc. would be
0.3x
0.01
1000
1000(N)
100 x
??
-
??
??
×
+
by condition,
0.3x
0.01 1000
0.3x 1000
100 x 200 x
??
-
??
??
=
++
?
0.3x 10 0.3x
100 x (200 x)
-
=
++
? (0.3x – 10) × (200 + x) = (0.3x)(100 +x)
? 60x – 2000 + 0.3 x
2
– 10x = 30x + 0.3x
2
? 20x  = 2000 ?  x = 100 ml
8. Compound A treated with NaNH
2
followed by CH
3
CH
2
Br gave compound B. Partial hydrogenation of compound B produced
compound C, which on ozonolysis gave a carbonyl compound D, (C
3
H
6
O). Compound D did not respond to iodoform test with
I
2
/Kl and NaOH. Find out the structures of A, B, C and D
A. Assuming 1 eq. of NaNH
2
is used,
Page 5

WBJEE - 2011 (Hints & Solutions) Physics & Chemistry

1. A shell of mass m is at rest initially. It explodes into three fragments having masses in the ratio 2 : 2 : 1. the fragments having
equal masses fly off along mutually perpendicular direction with speed V. What will be the speed of the third (lighter) fragment?
A.
From conservation of momentum
1
O2mv 2 mv =+
V
1
= 22v -
Hence, velocity of third part is 22v at an angle of 135
o
with either part.
2. A small spherical ball of mass m slides without friction from the top of a hemisphere of radius R. A T what height will the ball lose
contact with surface of the sphere ?
A. If the ball lose contact at B then, from conservation of energy.
mg cos?
mg sin?
R
R cos = h ?
R - R cos ?
N
mV
2
R
A
V
()
2
1
mgR 1 cos mv
2
-?=
v
2
= 2gR (1 – cos?) ......(i)
At B
2
mV
N mg cos
R
+= ?
When the ball will lose the contact
N = O
2
mv
mg cos
R
?=
DESCRIPTIVE TYPE QUESTIONS
SUB : PHYSICS & CHEMISTRY
WBJEE - 2011 (Hints & Solutions) Physics & Chemistry

V
2
= gR cos ? ........(ii)
? from (i) & (ii)
2Rg(1 - cos ) = gRcos ??
2 – 2 cos ? = cos ?.
2 = 3 cos ?.
? Height from the ground
h = R cos ? =
2R
3
3. Two identical cylindrical vessels, with their bases at the same level, each cotain a liquid of density p. The height of liquid in one
vessel in h
1
and that in the other is h
2
. The area of either base is A. What is the work done by gravity in equalizing the levels
when the vessles are interconnected ?
A.
P
h
1
A A h
2
?
Let find height = h
12
hh
h
2
+ ??
?=
??
??
decerese in height
12 1 2
1
hh h h
hh
22
+- ??? ?
?= - =
??? ?
??? ?
Mass of liquid
( )
12
hh
mA
2
-
=?
? Work done
12 12
hh hh
WA
22
?- ? - ?? ? ?
=?
?? ?? ??
?? ? ? ??
=
()
2
12
hh
gA
4
-
?
4. A battery of emf E and internal resistance r is connected across a pure resistive device (such as an electric heater) of resistance
R. Prove that the power output of the device will be maximum if R = r.
A. I
R
r
E
E
I
Rr
=
+
WBJEE - 2011 (Hints & Solutions) Physics & Chemistry

Power  P = I
2
R =
()
2
2
ER
Rr +
For maximum power
dp
0
dR
=
() ()
()
2
2
Rr .1 R.2Rr
E0
Rr4
??
+- +
= ??
+
??
??
R + r – 2R = 0
r = R
5. A radioactive isotope X with half life 1.5 × 10
9
yrs. decays into a stable nucleus Y . A rock sample contains both elements X and
Y in ratio 1 : 15. Find the age of the rock.
A.
X Y
t = 0, 16 0
t = 1, 1 15
9
1
2
T 1.5 10 yr =×
n
o
1
NN
2
??
=
??
??
1 = 16
n
1
2
??
??
??
n4
11
n4
22
?? ? ?
=?=
?? ? ?
?? ? ?
? time t = 4 × 1.5 × 10
9
= 6 ×10
9
yrs
6. The bacterial growth follows the rate l aw,
dN
KN
dt
=
where ‘K’ is a constant and ‘N’ is the number of bacteria cell at any time.
If the population of bacteria (no. of cell) is doubled in 5 minutes, find the time by which the population will be eight times of the
initial one.
A.
dN
KN
dt
=
(1st order kinetics)
? N = N
0
e
kt
(integrating)
? in 5 min, N = 2N
0
0
2.303 N
Klog
tN
=
WBJEE - 2011 (Hints & Solutions) Physics & Chemistry

?
o
0
2N 2.303
Klog
5N
??
=
??
??
min
–1

?
2.303
Klog2
5
=
for 8N
0

o
o
8N 2.303
tlog
2.303
N
log 2
5
??
??
=
??
??
??
??

?
53log2
t15min
log 2
×
==
? time required is 15 min.
7. In ‘x’ ml 0.3 (N) HCl, addition of 200 ml distilled water or addition of 100 ml 0.1 (N) NaOH, gives same final acid strength.
Determine ‘x’.
A. When 200 ml H
2
O is added to x ml solution
(x) (0.3) = (x + 200) (Y) ? final conc.
Y =
0.3x
200 x +
in 2nd case
Number of equivalents of  HCl after NaOH addition
0.3x
0.01
1000
-
( no of eq. of NaOH added = 0.01)
? conc. would be
0.3x
0.01
1000
1000(N)
100 x
??
-
??
??
×
+
by condition,
0.3x
0.01 1000
0.3x 1000
100 x 200 x
??
-
??
??
=
++
?
0.3x 10 0.3x
100 x (200 x)
-
=
++
? (0.3x – 10) × (200 + x) = (0.3x)(100 +x)
? 60x – 2000 + 0.3 x
2
– 10x = 30x + 0.3x
2
? 20x  = 2000 ?  x = 100 ml
8. Compound A treated with NaNH
2
followed by CH
3
CH
2
Br gave compound B. Partial hydrogenation of compound B produced
compound C, which on ozonolysis gave a carbonyl compound D, (C
3
H
6
O). Compound D did not respond to iodoform test with
I
2
/Kl and NaOH. Find out the structures of A, B, C and D
A. Assuming 1 eq. of NaNH
2
is used,
WBJEE - 2011 (Hints & Solutions) Physics & Chemistry

CH CH C  CH =
3 2
NaNH
2
– NH
3
CH CH C  C    Na =
3 2
– +
CH CH  – Br
3 2
S+
S–
S
N
2
? – NaBr
CH
3
CH
2
CH = CH CH
2
CH
3

Partial
Hydrogenation
????? ? CH
3
CH
2
C = C–CH
2
CH
3

(C) (B)
(i)  O
(ii)  Zn + H O
2
3
Ozonolysis
2 CH
3
CH
2
CHO  (No Keto Methyl group ? –ve iodoform)
(D)
9. An organic compound with molecular formula C
9
H
10
O forms, 2, 4-DNP derivative, reduces Tollen’s reagent and undergoes
Cannizzaro reaction. On vigorous oxidation it gives a dicarboxylic acid which is used in the preparation of terylene. Identify the
organic compound.
A. +ve  Brady’s test indicates carbonyl compound, Tollens & Cannizzaro reaction indicates aldehyde without a – H
? end product is terepthalic acid, compound must be
CHO
CH CH
3 2
[Strong oxidation]
COOH
COOH
(Terepthalic acid)
p-ethyl-benzaldehyde
```

## WBJEE Sample Papers, Section Wise & Full Mock Tests 2024

3 videos|10 docs|54 tests

### Up next

 Test | 240 ques

## FAQs on WBJEE Physics & Chemistry (Descriptive) - Previous Year Paper, 2011 - WBJEE Sample Papers, Section Wise & Full Mock Tests 2024

 1. What is the format of the WBJEE Physics & Chemistry (Descriptive) exam?
Ans. The WBJEE Physics & Chemistry (Descriptive) exam consists of descriptive questions that require students to provide detailed answers instead of choosing from multiple-choice options.
 2. Can you provide some tips for preparing for the WBJEE Physics & Chemistry (Descriptive) exam?
Ans. To prepare for the WBJEE Physics & Chemistry (Descriptive) exam, it is important to thoroughly understand the concepts and principles of physics and chemistry. Practice solving numerical problems and writing clear and concise explanations for various topics. Additionally, time management and effective revision techniques are crucial for success in this exam.
 3. What are the recommended study materials for the WBJEE Physics & Chemistry (Descriptive) exam?
Ans. Some recommended study materials for the WBJEE Physics & Chemistry (Descriptive) exam include NCERT textbooks, previous year question papers, reference books like Concepts of Physics by HC Verma and Physical Chemistry by OP Tandon. It is also advisable to solve sample papers and mock tests to familiarize yourself with the exam pattern and improve your writing skills.
 4. How should I approach the descriptive questions in the WBJEE Physics & Chemistry exam?
Ans. When answering descriptive questions in the WBJEE Physics & Chemistry exam, it is important to first understand the question thoroughly. Organize your thoughts and structure your answer in a logical manner. Use appropriate scientific terminology and provide clear explanations. Diagrams and equations should be labeled correctly and neatly. Practice writing answers within the given time limit to improve your speed and efficiency.
 5. Are there any specific topics that I should focus on for the WBJEE Physics & Chemistry (Descriptive) exam?
Ans. The WBJEE Physics & Chemistry (Descriptive) exam covers a wide range of topics from both physics and chemistry. It is important to have a strong foundation in all the major topics, including mechanics, thermodynamics, electrostatics, chemical bonding, organic chemistry, and more. Focus on understanding the fundamental concepts and their applications to solve problems and write comprehensive answers.

## WBJEE Sample Papers, Section Wise & Full Mock Tests 2024

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### Up next

 Test | 240 ques
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