Answer:
4.41 × 10¹² J, 2.72 × 10³ m³, 0.907 × 10 ⁻³ m
Explanation:
Gravitational potential energy is given by the formula: mgh
with m being the mass in kg, g reflecting the gravitational acceleration in m/s², and h indicating the distance above the dam's base.
The mass of the surface water amounts to: density of water × volume of water × 1 m = 1000 kg/m³ × 3.0 × 10⁶ m² × 1 m = 3 × 10⁹ kg
This leads to a total gravitational potential energy of 3 × 10⁹ kg × 9.81 m/s² × 150 m = 4.41 × 10¹² J
b) to find out how much water must flow through the dam to yield 1000 kW-hrs:
1,000 kW-hr = 3.6 × 10⁹ J
Given that the dam has a conversion efficiency of 90% for mechanical to electrical energy:
The necessary gravitational potential energy is 3.6 × 10⁹ J / 0.9 = 4 × 10⁹ J
The water mass needed is calculated using Energy required / gh = 4 × 10⁹ J / (9.81 m/s² × 150 m) = 2.718 × 10⁶ kg
To find the volume, we use density = mass/volume which gives us volume = mass/density = 2.718 × 10⁶ kg / (1000 kg/m³) = 2.72 × 10³ m³
The reduction in the lake's water level equals volume/area = 2.72 × 10³ m³ / (3.0 × 10⁶ m²) = 0.907 × 10 ⁻³ m