Question

The average solar energy incident on the green canopy (leaves) of a tree is ${10}^{8}J$ per day. The wood of $12.5kJ/g$ calorific value is obtained from tree. If tree could convert $1\%$ of incident solar energy as wood then how many days will it take to produce 12 kg of wood?

• A.
  120 days
• B.
  60 days
• C.
  90 days
• D.
  150 days

Answer 1

The correct option is D

150 days
Calorific value of wood $=12.5kJ/g=12.5\times {10}^{3}J/g$

Average energy incident $={10}^{8}Jperday1\%\text{of this energy will be used to}producewood.E=1\%of{10}^8\text{J per day J per day}=\frac{1}{100}\times {10}^8={10}^{6}Jperday.$

$\text{Energy required to produce 12 kg of wood = Calorific value}\times 12\times {10}^3[12kg=12\times {10}^{3}g]=12.5\times {10}^3\times 12\times {10}^{3}J$

So, number of days required to produce 12 kg wood
$=\frac{12.5\times {10}^3\times 12\times {10}^3}{{10}^6}=150days$

Hence, the correct answer is option (d).