Transformações de Energia – Energia Mecânica – EN
Commented Resolution
Energy Transformations – Mechanical Energy
01- It transforms the gravitational potential energy of the water on the surface of the dam of height h into kinetic energy (of movement) in the turbine. The turbine drives the generator which, in turn, transforms kinetic energy into electrical energy — R- D
02- I. Correct — the function of the steam obtained by nuclear fission is to turn the turbine.
II. Correct — according to the statement, the kinetic energy acquired by the turbine, when rotating due to the steam, is transferred to the generator, where it is transformed from kinetic to electrical.
III. False — the function of the condensation chamber is to liquefy the steam by cooling it and turning it into water, which is then pumped back into the reactor.
R-D
03- I. Correct — the increase in the temperature of a liquid decreases the solubility of the gases (including oxygen) contained in it.
II. Correct — since fish are poikilothermic animals (temperature varies according to the environment in which they are found), changes in water temperature affect their metabolism and, depending on the intensity of the change, may result in their death.
III. False — the increase in water temperature favors the increase of microorganisms (bacteria and algae), harming the development of vegetation.
R-D
04- While walking, the back and forth movements of the hips going up and down causes the transformation of elastic potential energy stored in the springs into kinetic energy — this kinetic energy, in turn, during the going up and down, compresses and stretches the springs even more, restoring the elastic potential energy and so on — thus, while walking there is a transformation of potential energy into kinetic energy and vice versa — this up and down movement (kinetic energy) turns the motor, which in turn turns the generator, transforming this kinetic energy into electrical energy — A- A
05- At the moment the arrow is released, all elastic potential energy stored in the bowstring and consequently in the arrow, is transformed into movement energy (kinetic energy) of the arrow — R- C
06- It transforms the gravitational potential energy of the water on the surface of the dam of height h into kinetic energy (of movement) in the turbine, which drives the generator, which transforms this kinetic energy into electrical energy — R- B
07- Fossil fuels are substances composed of carbon, used as a source of energy
— coal, oil and natural gas are responsible for around 85% of the energy produced in the world — in thermoelectric plants, it is common to use oil, a fossil fuel whose formation period is very long (millions of years) — R- E
08-
I. correct — as Brazil has the most immense, abundant and extensive amounts of river basins on planet Earth, these should be used with the construction of hydroelectric plants, as this immense amount of water constitutes renewable sources.
II. False — the damming of water in the normal course of rivers, caused by large hydroelectric plants, has environmental impacts — it floods forest areas, damaging terrestrial flora and fauna with the loss of vegetation, acidifies the water, etc.
III. False — the evaporation of water from a dam is too small to cause rain.
A- A
09- Energy is neither created nor destroyed, only transformed — it is conserved in all processes (Principle of Conservation of Energy) — A- A
10- The statement requires less environmental impact — since solar incidence in the region is high, the best way to obtain energy is photovoltaic (generation of electrical energy with renewable energy from the Sun) — R- D
11- Mass of coal required to obtain 200,000 MWh of energy (200.10 6 kWh) — rule of three — 1 kg — 10 kWh — m — 200.10 6 kWh — m=200.10 6 /10 — m=20.10 6 =20,000,000 kg=20,000 tons — number of trucks that will transport this mass — another rule of three — 1 truck — 10 tons — n trucks — 20,000 tons — n=20,000/10 — n=2,000 trucks — R- D
12- Data — power of radiation emitted by the Sun — PoSun = 200 billion MW = 200.10 9 .10 6 = 2.10 17 W — power harnessed in the form of electricity — Poelet . = 500,000MW = 500.10 3 .10 6 = 5.10 11 W — the fraction (f) of energy harnessed in the form of electricity corresponds to the ratio — f = PoSun / Poelet . = 5.10 11 / 2.10 17 — f = 2.5 10 -6 — R- B
13-
Note in the diagram above that, since 1% was evaporated, the total power released by the burning of fuel in the tank was P ototal = 71kW — power dissipated from that released by the tank — 
P odiss. = 56.8kW — power actually used — P outil = 14.2kW — the dissipated fraction of energy corresponds to the relationship — f = P odiss. /P ototal = 56.8/71 — f = 0.8 — 80% of energy is dissipated —
A- A
14- Inside the engine, chemical combustion reactions occur (combustion or burning is a chemical reaction between a substance (the fuel) and a gas (the oxidizer), usually oxygen), with the release of heat and light — in this case, the fuel is gasoline, alcohol, or natural gas (NGV and the oxidizer is the oxygen present in the air — the gases resulting from these reactions have high temperatures and pressures, releasing enormous amounts of heat and light.
pressure forces that move the pistons, which are attached to the axles of the wheels, turning them, making the car move — R- A .