COMEDK Exam 2014 Solved Paper

According to Newton's law of cooling,

T1−T2

t

=K(

T1+T2

2

−Ts).........(i)
where, Ts is the temperature of surrounding.
For the first case, T1=94°C,T2=86°C
t=2min=120s,Ts=20°C
∴ Putting these values in Eq. (i), we get

94−86

120

=K(

94+86

2

−20)
⇒ K=

8

120×70

.............(ii)
For the second case, T1=86°C,T2=74°C
∴ From Eq.(i), we get
86−

74

t

=K(

86+74

2

−20)
⇒

12

t

=

8

120×70

(60)
⇒ t=210s