Question

An iron casting of mass 30kg at 400oC is being cooled and it 

gives out heat on an average of 920J/s. Calculate its temperature 

after 1 hour? (Specific heat capacity of iron = 460Jkg -1oC

 -1). 

Answer 1

We know,

Heat change, $H = m s ∆t$

m = mass of iron cast

= 30kg

s = Specific heat capacity of iron

= 460Jkg -1oC-1

$∆t = initial temperature - final temperature$

$= (400- x) °C$

$x = temperature after 1 hour$

So, $H = 30×460×(400-x)$

The cast release heat on the rate ,

$h = 920J/s$

So,

amount of heat release in 1 hour,

$H = h × 3600 s$

$= 920 J/s × 3600 s$

$= 3312000 J$

$=3312×10³ J$

So,

$$3312×10³ = 30×460×(400-x)$$

$Or, 400-t = 240$

$Or, t = 160$

Hence, its temperature after 1 hour = 160 °C