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NEET 2021 Physics and Chemistry
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© examsnet.com
Question : 13
Total: 100
A cup of coffee cools from 90°C to 80°C in t minutes, when the room temperature is 20°C. The time taken by a similar cup of coffee to cool from 80°C to 60°C at a room temperature same at 20°C is
[NEET 2021]
13
10
t
13
5
t
10
13
t
5
13
t
Validate
Solution:
👈: Video Solution
From Average form of Newton's law of cooling
−
(
T
1
+
T
2
2
−
T
s
)
K
=
T
1
−
T
2
Δ
t
T
1
and
T
2
are initial and final temperature and
T
s
is surrounding temperature.
⇒
−
K
[
(
90
+
80
)
2
−
20
]
=
90
−
80
t
⇒
−
K
(
65
)
=
10
t
⇒
K
=
−
2
13
t
In second case,
−
K
(
80
+
60
2
−
20
)
=
(
80
−
60
)
t
1
⇒
−
K
(
50
)
=
20
t
1
⇒
2
13
t
(
50
)
=
20
t
1
⇒
t
1
=
13
t
5
© examsnet.com
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