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WBJEE 2019 Physics Solved Paper
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© examsnet.com
Question : 32
Total: 40
A horizontal fire hose with a nozzle of cross-sectional area
5
√
21
×
10
−
3
m
2
delivers a cubic metre of water in 10s. What will be the maximum possible increase in the temperature of water while it hits a rigid wall (neglecting the effect of gravity) ?
1°C
0.1 °C
10°C
0.01 °C
Validate
Solution:
Given, cross sectional area of nozzle
A
=
5
√
21
×
10
−
3
m
2
and rate of heat transfer
Q
=
1
10
=
10
−
1
m
3
/
s
∵ Heat transfer Q = AV
∴
V
=
Q
A
=
10
−
1
m
3
∕
s
5
√
21
×
10
−
3
m
2
=
2
√
21
×
10
m
/
s
When it hits a rigid wall then maximum possible increase in temperature of water can be expressed as
1
2
m
v
2
=
m
s
∆
T
....(i)
where,
m = mass,
s = specific heat of water
=
1
c
a
l
/
g
=
42
×
10
3
J
/
k
g
and
∆
T
=
increase in temperature
From
E
q
⋅
(
i
)
,
∆
T
=
1
2
v
2
s
=
(
2
√
21
×
10
1
)
2
2
×
4.2
×
10
3
=
84
×
10
2
8.4
×
10
3
=
1
∘
C
© examsnet.com
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