Question

A metal block is made from a mixture of $2.4 \,kg$ of aluminium, $1.6 \,kg$ of brass and $0.8 \,kg$ of copper. The amount of heat required to raise the temperature of this block from $20^{\circ} C$ to $80^{\circ} C$ is (specific heats of aluminium, brass and copper are $0.216,0.0917$ and $0.0931$ cal kg $^{-1}{ }^{\circ} C ^{-1}$, respectively)

• A. 96.2 cal
• B. 44.4 cal
• C. 86.2 cal
• D. 62.8 cal

Answer 1

Answer: (B)

Given, $m_{1}=2.4 \,kg , m_{2}=1.6 \,kg , m_{3}=0.8 \,kg$
$s_{1}=0.216 \,cal \,kg { }^{-1 \circ}\, C ^{-1}, $
$s_{2}=0.0917 \,cal\, kg { }^{-1 \circ} \,C ^{-1}$,
$s_{3}=0.0931\,cal\, kg { }^{-1 \circ} \,C ^{-1}$
and $\Delta T=T_{2}-T_{1}=(80-20)^{\circ} C =60^{\circ} C$
$ Q =m_{1} s_{1} \Delta \theta+m_{2} s_{2} \Delta \theta+m_{3} s_{3} \Delta T $
$=(2.4 \times 0.216+1.6 \times 0.0917+0.8 \times 0.0931)(60) $
$=44.376\, cal \approx 44.4 \,cal $