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KCET 2016 Physics Solved Paper
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© examsnet.com
Question : 11
Total: 60
A pan filled with hot food cools from 94 °C to 86 °C in 2 minutes. When the room temperature'is 20 °C. How long will it cool from 74 °C to 66 °C ?
2 minutes
2.8 minutes
2.5 minutes
1.8 minutes
Validate
Solution:
Given, food cools from 94 °C to 86 °C in 2 minutes; room temperature = 20 °C
Now,
d
T
d
t
=
k
(
θ
−
θ
0
)
For 1st case,
d
T
d
t
=
94
−
86
2
=
8
2
=
4
∘
and
(
θ
−
θ
0
)
=
(
94
+
86
)
2
−
20
∘
=
70
∘
∴
4
=
k
to
⇒
k
=
4
70
For 2nd case,
d
T
d
t
=
74
−
66
t
=
8
t
and
θ
−
θ
0
=
(
74
+
66
)
2
−
20
=
50
∘
∴
8
t
=
4
70
×
50
⇒
t
=
8
×
70
4
×
50
=
2.8
Thus, food cools from 74 °C to 66 °C in 2.8 minutes
© examsnet.com
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