Answer:
1) 7 × 10⁹ MJ of energy
2) 48.611 days
Explanation:
Given:
Electricity produced by the dam = 2 × 10⁹ W
Concrete in dam = 7 × 10⁹ Kg
also,
1 MJ energy is required to produce 1 kg
or
1 × 10⁶ J is required to produce 1 kg
1) Now, the energy required for 7 × 10⁹ Kg = 7 × 10⁹ × 1 × 10⁶
or
= 7 × 10⁹ MJ of energy
2) Energy produced = 2 × 10⁹ W = 2 × 10⁹ J/s
Now,
energy payback time =
![\frac{\textup{Energy required}}{\textup{Energy produced}}](https://img.qammunity.org/2020/formulas/mathematics/college/f67900cncr40oa6kgh1ugv6yl2uomoh42o.png)
or
energy payback time =
![(7*10^9\ MJ)/(2*10^9\ J/s)](https://img.qammunity.org/2020/formulas/mathematics/college/vmhhn4dvsupgh7vets8tq1x0g7p5g1zw60.png)
or
energy payback time = 3.5 × 10⁶ seconds
now,
1 day = 24 × 60 × 60 seconds = 72000 seconds
thus,
3.5 × 10⁶ seconds =
= 48.611 days