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  4. The energy supplied to Kolkata by the state electricity board during an average November week day was 40 GWh. If this energy could be obtained by the conservation of matter, how much mass would have to be annihilated?

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Q. The energy supplied to Kolkata by the state electricity board during an average November week day was $40 \,GWh$. If this energy could be obtained by the conservation of matter, how much mass would have to be annihilated?

BHUBHU 2006

Solution:

$E=40\, G W h=\left(40 \times 10^{9} \,J / s \right)$
$(60 \times 60\, s )=1.44 \times 10^{14} \,J$
But $E=m c^{2}$
so, $m=\frac{E}{c^{2}}=\frac{1.44 \times 10^{14}}{\left(3 \times 10^{8}\right)^{2}} $
$=1.6 \times 10^{3}\, kg$
i.e., $m=1.6\, g$