Answer:
4.41 × 10¹² J, 2.72 × 10³ m³, 0.907 × 10 ⁻³ m
Explanation:
Gravitational potential energy = mgh
where m is mass in kg, g is acceleration due to gravity in m/s², and h is the distance from the base of the dam.
mass of the surface water = density of water × volume of water × 1 m = 1000 kg / m³ × 3.0 × 10⁶ m² × 1 m = 3 × 10⁹ kg
Gravitational potential energy = 3 × 10⁹ kg × 9.81 m/s² × 150 m = 4.41 × 10¹² J
b)what volume of water must pass through the dam to produce 1000 kw-hrs
1 000 kw-hr = 3.6 × 10 ⁹ J
the dam has mechanical energy conversion of 90% to electrical energy
Gravitational potential energy needed = 3.6 × 10 ⁹ J / 0.9 = 4 × 10⁹ J
mass of water needed = Energy required / g h = 4 × 10⁹ J / (9.81 m/s² × 150 m) = 2.718 × 10 ⁶ kg
density = mass / volume
volume = mass / density = 2.718 × 10 ⁶ kg / (1000 kg/ m³) = 2.72 × 10³ m³
the distance the level of the water in the lake fell = volume / area = 2.72 × 10³ m³ / (3.0×10⁶ m²) = 0.907 × 10 ⁻³ m
Torque is equal position vector times (r) times force vector
(F). Since F= 10 N and r = 0.1 m, so the
torque is equal to (10 N) x ( 0.1 m) = 1Nm. The direction of the torque would
be into the screen, clockwise rotation.
Answer:
best explanation of this is sentence B
Explanation:
The radiation emission of the bodies is given by the expression
P = σ A e T⁴
Where P is the power emitted in watts, σ is the Stefan-Boltzmann constant, A is the surface area of the body, e is the emissivity for black body e = 1 and T is the absolute body temperature in degrees Kelvin.
When the values are substituted the power is quite high 2.5 KW, but the medium surrounding the box also emits radiation
T box ≈ T room
P box ≈ P room
As the two powers are similar and the box can absorbed, since it has the ability to emit and absorb radiation, as the medium is also close of the temperature of the box, the amount emitted is very similar to that absorbed, so the net change in energy is very small.
In the case that the box is much hotter or colder than the surrounding medium if there is a significant net transfer.
Consequently, the best explanation of this is sentence B
