UPSEE Solved Model Paper 3

From the Newtons law of cooling
Rate of cooling α difference in temperature

dT

dt

α Δθ
⇒ dTdt = KΔθ
In first case dT = 61 - 59 = 2
Δθ = 50 - 30 = 20 dt
= 4 min
∴ K =

1

Δθ

(

dT

dt

) =

2

30×4

=

1

60

For second case, dT = 2Δθ = 50 - 30 = 20
∴ dt =

1

K

(

dT

dθ

) =

2

1 60 ×20

= 6 min