The Natural Sciences and its Technologies test, in which Physics is inserted, is composed of 45 objective questions, with 5 answer alternatives in each one of them.
As the total number of questions is divided into the disciplines of Physics, Chemistry and Biology, there are around 15 questions for each of them.
The statements are contextualized and frequently address issues related to everyday life and scientific innovations.
Contents that fall the most in the Physics test
In the infographic below we list the most charged content in the Physics test.
1. mechanics
Motion, Newton's laws, simple machines and hydrostatics are some of the contents demanded in this area of Physics.
A good understanding of the concepts behind the laws, in addition to knowing how to characterize the movements, their causes and consequences, is essential to be able to solve the problem-situations proposed in the questions.
Below is an example of a question related to this content:
(Enem/2017) In a head-on collision between two cars, the force that the seat belt exerts on the driver's chest and abdomen can cause serious damage to the internal organs. With the safety of its product in mind, a car manufacturer conducted tests on five different belt models. The tests simulated a 0.30-second collision, and the dolls representing the occupants were equipped with accelerometers. This equipment records the modulus of the doll's deceleration as a function of time. Parameters such as doll mass, belt dimensions and speed immediately before and after impact were the same for all tests. The final result obtained is in the graph of acceleration by time.
Which belt model offers the lowest risk of injury to the driver?
to 1
b) 2
c) 3
d) 4
e) 5
Correct alternative b) 2.
Note that this issue presents a problem-situation related to safety equipment that we use in our daily lives.
This is a matter of dynamics, where we need to identify the relationships between the quantities associated with the situation. In this case the quantities are force and acceleration.
We know from Newton's second law that force is directly proportional to the product of mass and acceleration.
As in all experiments, the passenger's mass is the same, so the greater the acceleration, the greater the force that the belt will exert on the passenger (braking force).
After identifying the quantities and their relationships, the next step is to analyze the graph presented.
If we are looking for the belt that offers the least risk of injury, then it will have to be the one with the least acceleration, since in the problem statement itself it is signaled that the greater the force, the greater the risk of injury.
Thus, we reach the conclusion that it will be belt number 2, as it is the one with the least acceleration.
2. Electricity and Energy
This topic includes an important law of physics, which is energy conservation, in addition to electrical phenomena that are very present in everyday life and are always charged in the test.
Knowing how to correctly recognize the different energy transformations that can occur throughout a physical process will be essential to resolve several issues related to this content.
Very often, electricity issues demand the sizing of electrical circuits and knowing applying the formulas for voltage, equivalent resistance, power and electrical energy will be very important.
Check below a question that fell on Enem related to this content:
(Enem/2018) Many smartphones and tablets no longer need keys, since all commands can be given by pressing the screen itself. Initially, this technology was provided through resistive screens, basically formed by two layers of conductive material that do not touch until someone presses them, modifying the total resistance of the circuit according to the point where the Touch. The image is a simplification of the circuit formed by the boards, in which A and B represent points where the circuit can be closed through touch.
What is the equivalent resistance in the circuit caused by a touch that closes the circuit at point A?
a) 1.3 kΩ
b) 4.0 kΩ
c) 6.0 kΩ
d) 6.7 kΩ
e) 12.0 kΩ
Correct alternative c) 6.0 kΩ.
This is a question of applying electricity to a technological resource. In it, the participant must analyze the circuit by closing only one of the switches presented in the diagram.
From there, it will be necessary to identify the type of resistor association and what happens to the variables involved in the proposed situation.
Since only switch A has been connected, then the resistance connected to terminals AB will not be working. In this way, we have three resistors, two connected in parallel and in series with the third.
Finally, by correctly applying the formulas for calculating the equivalent resistance, the participant will find the correct answer, as indicated below:
First we calculate the equivalent resistance of the parallel connection. As we have two resistances and they are equal, we can use the following formula:
The equivalent resistance of the parallel association is associated in series with the third resistance. Therefore, we can calculate the equivalent resistance of this association by doing:
Req = Rparallel + R
Replacing the resistance values, we have:
Req= 2 + 4 = 6 kΩ
3. undulatory
In order to get the questions related to this subject right, the participant must be able to recognize the events and use of wave phenomena in everyday life.
Knowing how to apply the fundamental equation of the undulatory, identifying the relationships between the quantities involved and knowing the various undulatory phenomena are fundamental requirements.
See how this content is charged on Enem, following the example below:
(Enem/2018) The sounder is a physical device implanted on the surface of a highway in a way that causes vibration and noise when a vehicle passes over it, alerting to the atypical situation ahead, such as works, tolls or crossing of pedestrians. When passing over the sounders, the vehicle's suspension undergoes vibrations that produce sound waves, resulting in a peculiar noise. Consider a vehicle that passes at a constant speed equal to 108 km/h over a sounder whose tracks are separated by a distance of 8 cm.
The frequency of the car's vibration perceived by the driver while passing this sounder is closer to
a) 8.6 hertz.
b) 13.5 hertz.
c) 375 hertz
d) 1350 hertz.
e) 4860 hertz.
Correct alternative c) 375 hertz.
The question relates sound waves with uniform motion. Therefore, we will use the velocity formula for this type of movement and the relationship between frequency and time.
It is important to highlight that the participant must, always in Physics issues, be aware of the measurement units. In this matter, neither speed nor distance are in the international system of measurements.
Therefore, this must be done so that it is possible to correctly find the frequency value.
Remembering that to transform km/h into m/s just divide by 3.6 and to transform cm into m we must divide by 100.
Therefore, the problem data will be:
v = 108 k/h = 30 m/s
d = 8 cm = 0.08 m
Considering that the speed of the car passing the sounder is constant (uniform movement), we will use the formula of speed to find the amount of time the car will take to pass between two consecutive lanes, or be:
The sound vibration will be produced each time the car passes through the lanes, so the period of the wave will be equal to the value we found for the time.
We also have that the frequency of a wave is equal to the inverse of the period, so its value will be equal to:
4. Thermodynamics
In this subject, once again it is essential to understand the energy transformations, as issues that associate thermal energy with other types of energy are very common.
Furthermore, knowing the laws of thermodynamics and the operation of thermal machines and refrigerators is also important.
See a question in which this knowledge was charged:
(Enem/2016) The internal combustion engine, used to transport people and cargo, is a thermal machine whose cycle consists of four stages: admission, compression, explosion/expansion and exhaust. These steps are represented in the pressure versus volume diagram. In gasoline engines, the air/fuel mixture is combusted by an electric spark.
For the described engine, at what point in the cycle is the electric spark produced?
a) A
b) B
c) C
d) D
and is
Correct alternative c) C.
To resolve this issue, it is necessary to analyze the graph and associate each phase of the cycle with the indicated points. Knowing the graph of the different transformations indicated helps to understand these phases.
In the statement it is indicated that each cycle is formed by 4 different stages, namely: admission, compression, explosion/expansion and exhaust.
We can conclude that the intake is the phase in which the engine increases the fluid volume inside. We note that this step takes place between points A and B.
Between points B and C there is a reduction in volume and an increase in pressure. This phase corresponds to an isothermal compression (remembering the type of relationship between the quantities temperature, pressure and volume).
From point C to point D, the graph shows an increase in pressure, but without changing the volume. This happens thanks to the increase in temperature, due to the explosion caused by the electric spark.
Therefore, the spark occurs at the beginning of this step, which in the graph is represented by the letter C.
5.Optics
Once again, it is essential to understand the concepts, which in this case are related to light and its propagation.
Having the ability to apply this knowledge in a variety of contexts will make you more likely to get the questions related to that content right.
It is also important to know how to correctly interpret the statement of the question, the images and the graphics, as it is common that the answer to the question can be found through this analysis.
Check below an optical question that was charged on Enem:
(Enem/2018) Many primates, including us humans, have trichromatic vision: three visual pigments in the retina sensitive to light of a certain range of wavelengths. Informally, although the pigments themselves have no color, these are known as "blue", "green" and "red" pigments and are associated with the color that causes great excitation (activation). The sensation we get when looking at a colored object is due to the relative activation of the three pigments. That is, if we stimulated the retina with a light in the range of 530 nm (rectangle I in the graph), we would not excite the "blue" pigment, the “green” pigment would be activated at the maximum and “red” would be activated at approximately 75%, and this would give us the sensation of seeing a color yellowish. On the other hand, light in the 600 nm wavelength range (rectangle II) would stimulate the “green” pigment a little and the “red” by about 75%, and this would give us the sensation of seeing reddish-orange. However, there are genetic characteristics present in some individuals, collectively known as color blindness, in which one or more pigments do not function perfectly.
If we stimulated the retina of an individual with this characteristic, who did not have the pigment known as "green", with the lights of 530 nm and 600 nm in the same light intensity, this individual would be unable to
a) identify the wavelength of yellow, since it does not have the "green" pigment.
b) see the orange wavelength stimulus, as there would be no stimulation of a visual pigment.
c) detect both wavelengths, since pigment stimulation would be impaired.
d) visualize the purple wavelength stimulus, as it is at the other end of the spectrum.
e) distinguish the two wavelengths, as both stimulate the “red” pigment at the same intensity.
Correct alternative e) distinguish the two wavelengths, as both stimulate the “red” pigment at the same intensity.
This issue is basically resolved by the correct analysis of the proposed diagram.
The statement states that for the person to perceive a certain color, it is necessary that the activation of certain "pigments" and that in the case of color blind some of these pigments do not work correctly.
Therefore, people with color blindness cannot distinguish certain colors.
Observing rectangle I, we identified that when stimulating with a light in the range of 530 nm, the person with color blindness will only have activation of the "red" pigment, with an intensity of approximately 75%, as the "blue" is outside this range and it has no pigment "green".
Note that the same happens with light in the 600 nm range (rectangle II), so the person is not able to distinguish different colors for these two wavelengths.
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