Question

The useful energy available by burning $1g$ coal is $2kcal$. The cost of producing $1Wh$ energy is (1 kg coal costs 1 paise)

• A. 9 paise
• B. 18 paise
• C. 4.5 paise
• D. 36 paise

Answer 1

Answer: (A)

9 paise

For 2 kcal or 8400 joules, 1 gm coal is needed for 1 kWh
or $3.6\times {10}^6$ joules coal needed
$=\frac{3.6\times {10}^6}{8400}gms=\frac{3}{7}kg.$
Since, 1 kg coal cost 21 paise
$\therefore \frac{3}{7}kgcoalwillcost=\frac{3}{7}\times 21=9paise$