Enem – Mec – 2021 – EN
ENEM – MEC – 2021
ENEM – MEC – 2021
Compare this and other resolutions from ENEM 2021 and from the entrance exams of other Universities at fisicaevestibular.com.br with others and you will see that it:
It has a better look and more informative illustrations.
It was made for students who really have difficulties with Physics and Mathematics concepts, always trying to explain the smallest details.
It doesn’t just include formulas, always trying to show their origins and uses.
Whenever necessary, he tries to explain through drawings and illustrations.
Don’t skip steps explaining sequence by sequence.
There is a great deal of concern that the student understands the solutions. The teacher puts himself in the student’s shoes.
It often provides information beyond that needed for resolutions, but is useful in future enens.
And much, much more.
The National High School Exam (Enem) is a test created in 1998 by the Brazilian Ministry of Education (MEC) that is used as a tool to assess the overall quality of high school education in the country. Later, the exam began to be used as an entrance exam for higher education in Brazilian public universities through SiSU (Unified Selection System).
Enem is the largest exam in Brazil, with more than 8.2 million applicants in 2016.
The Enem score can be used as access to higher education in Brazilian universities that have adopted Enem as the sole or partial form of selection.
Each university has the autonomy to adhere to the new Enem as it deems best.
Along the same lines as Prouni, the Unified Selection System (SiSU) is completely online and will allow students to choose courses and places among participating higher education institutions that will use Enem as the only form of admission.
The grade is also used by people interested in earning points for the University for All Program (Prouni).
Participation in the test serves as certification of completion of high school for people over 18 years of age.
A boy needs to build a circuit that turns on three different colored bulbs, one at a time.
It has the bulbs, wires, a battery and two switches as illustrated, along with its three-dot symbol. When this switch closes AB, it opens BC and vice versa.
The boy made five electrical circuits using the two switches, but only one satisfied his need. This circuit is represented by
The connection possibilities, since when one opens and the other closes are : AB with AB; AB with BC; BC with BC and BC with AB.
In each case, according to the statement, only one lamp can light up.
Analyzing each alternative and remembering that the electric current i leaves the positive pole and only passes through the lamp when the circuit is closed, with it returning to the negative pole.
the)
b)
W)
d)
and)
The only alternative that satisfies turning on a single bulb at a time is (d)
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02- (ENEM – MEC – 021)
Consider the comic strip, in the situation where the temperature of the environment is lower than the body temperature of the characters.
WATTERSON. B. Available at: https://novaescola.org.br. Accessed on: August 11, 2014.
The discomfort mentioned by the character in the comic strip is due to the fact that, on humid days,
a) the temperature of the water vapor present in the air is high.
b) sweat has greater difficulty evaporating from the body.
c) the rate of radiation absorption by the body becomes greater.
d) the air becomes a poor conductor and hinders the heat release process.
e) water vapor present in the air condenses when it comes into contact with the skin.
The discomfort mentioned by the character in the comic strip is due to the fact that, on humid days,
Note in the statement that the discomfort (thermal sensation of heat) mentioned by the character in the comic strip is due to the fact that it occurs on humid days and, in the comic strip , Calvin states that it is hot with Harold responding that what bothers him most is the humidity .
To reduce the sensation of heat, you need to sweat so that the evaporation of sweat from the skin removes heat from the body, cooling it down.
However, as the day is humid and the relative humidity is higher (more water vapor in the air), it becomes more difficult for the body’s sweat to evaporate , providing relief from the heat and cooling the body.
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03- (ENEM – MEC – 021)
In the city of São Paulo , heat islands are responsible for changing the direction of the sea breeze flow that should reach the source region.
But as the sea breeze crosses the heat island, it now encounters a vertical airflow , which transfers to it thermal energy absorbed from the city’s hot surfaces, moving it to higher altitudes.
This way, there is condensation and heavy rain in the city center, instead of in the source region.
The image shows the three subsystems that exchange energy in this phenomenon.
In the process of heavy rains in the center of the city of São Paulo, there are two dominant mechanisms of heat transfer: between the Sun and the heat island, and between the heat island and the sea breeze.
VIVEIROS. M. Heat islands divert rain from dams. Available at: www2.feis.unesp.br.
Accessed on: December 3, 2019 (adapted).
These mechanisms are, respectively,
a) irradiation and convection.
b) irradiation and irradiation.
c) conduction and irradiation.
d) convection and radiation.
e) convection and convection
If you haven’t mastered the theory, here it is:
Thermal irradiation
Thermal convection
This is the transfer of thermal energy (heat) through moving matter due to the difference in densities of that matter.
In the case of exercise, the transfer of heat between the Sun and the heat island occurs through radiation (or irradiation) with infrared electromagnetic waves (heat waves) emitted by the Sun passing through the vacuum and then the air and reaching the heat island (in this case, downtown São Paulo).
The heat transfer from the heat island (center of São Paulo) and the sea breeze occurs with the rise of hot air emitted by the heat island, through convection reaching the air from the sea breeze, heating it and raising it as well.
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04 – (ENEM – MEC – 021)
In his study on falling bodies, Aristotle stated that if we drop light and heavy bodies from the same height, the heavier one would reach the ground faster.
This idea is supported by something that is difficult to refute, direct observation of reality based on common sense.
After a physics class, two classmates were arguing about falling bodies, and one tried to convince the other that he was right:
Colleague A: “ A heavier body falls faster than a lighter one when dropped from the same height. I prove it by dropping a stone and a cork. The stone arrives first. There you have it! It’s proven!”
Colleague B: I don’t think so! I picked up a sheet of paper and dropped it. When I crumpled it, it fell faster. How is that possible? If it was the same sheet of paper, it should have fallen the same way. There has to be another explanation!”
HÜLSENDEGER, M, An analysis of students’ conceptions about falling bodies.
Brazilian Journal of Physics Teaching, No. 3, Dec. 2004 (adapted).
The common physical aspect that explains the difference in behavior of falling bodies in this discussion is
a) weight of the bodies.
b) air resistance.
c) mass of the bodies.
d) density of bodies.
e) acceleration of gravity.
Air resistance force
We call free fall the fall of bodies disregarding air resistance. If there is air resistance it will not be free fall.
Disregarding the air, all bodies, regardless of their shape or mass, close to the Earth’s surface (approximately up to 8 km high), fall with the same acceleration (of gravity) which, within that height, is approximately 9.8 m/s 2 , which we can round up to 10 m/s 2 .
Example; An ant with mass m f and an elephant with mass M e , in free fall, without air:
Thus, disregarding air resistance, an elephant and an ant, when dropped from the same height, reach the ground at the same time.
However, when bodies move in a fluid (air or water) , in addition to the weight, which is constant , a force also appears , contrary to the movement, which we call the air resistance force ( ) , which depends on the speed of the body, its shape and the cross-sectional area in relation to the direction of movement in this medium, which influences the time of fall.
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05- (ENEM – MEC – 021)
TEXT I
In the cordel entitledLord of the Rings, written by Gonçalo Ferreira da Silva, the sextet reads:
The distance in relation
To our beloved planet
A little less than that of the Sun
He is distanced
And less dense than water
When in normal state
MEDEIROS. A.; AGRA. JTM, Astronomy in the literature of
cordel. Physics at School, n. 1, April, 2010 (fragment).
TEXT II
Average distances of the planets from the Sun and their average densities
Characteristics of the planets. Available at astronco.com. Access
on: 8 Nov 2019 (adapted).
Considering the verses of the sextet and the information in the table, which planet does the cordel refer to?
a) Mercury.
b) Jupiter.
c) Uranus.
d) Saturn.
e) Neptune.
The statement states that this planet is less dense than water in its normal state (liquid) whose density is 1.0 and, from the table provided, you can see that the only planet that satisfies this condition is Saturn (0.7).
Or even, by the title Lord of the Rings where, although Saturn is not the only planet with rings, it is
which has its most prominent rings, known as “Saturn’s rings”.
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06- (ENEM – MEC – 021)
Scientists at the University of New South Wales in Australia demonstrated in 2012 that Ohm’s Law is valid even for very thin wires, whose cross-sectional area comprises just a few atoms. The table shows the areas and lengths of some of the wires constructed (respectively with the same units of measurement).
Consider that the resistivity remains constant for all geometries (an approximation confirmed by the study).
WEBER. S.B, et. al Ohm’s Law Survives the Atomic Scale.
Science. n. 335. Jan. 2012 (adapted).
The electrical resistances of the wires, in increasing order, are
This question in which resistivity appearsrefers to Ohm’s second law given below:
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07- (ENEM – MEC – 021)
Two spheres charged with charges of equal magnitude and opposite signs are connected by a rigid insulating rod in the shape of a dumbbell.
THEsystem moves under the action of gravity in a region that has a uniform horizontal magnetic field 
, from left to right.
The image shows the system seen from top to bottom, in the same direction as the acceleration of gravity ( 
) that acts in the region.
Seen from above , the schematic diagram of the magnetic forces acting on the system, at the initial moment when the charges penetrate the magnetic field region, is represented in
Since the other charge is negative, the magnetic force on it has the same direction (vertical) but opposite to that of the positive charge (upwards).
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08- (ENEM – MEC – 021)
When setting up a kitchen for a restaurant, choosing the correct material for the pans is
important, because the pan that conducts more heat is able to cook food more quickly and, therefore, there is a saving of gas .
The ascending order from most economical to least economical is
a) copper-steel, aluminum and iron.
b) aluminum, copper-steel and iron.
c) copper-steel, iron and aluminum.
d) aluminum, iron and copper-steel.
e) iron, aluminum and copper-steel.
According to the statement, the pan that conducts more heat is able to cook food more quickly and, therefore, there is a saving of gas.
09- (ENEM – MEC – 021)
An electrocardiogram is a cardiac exam that measures the intensity of electrical signals coming from the heart.
The image shows the typical result obtained in a healthy patient and the signal intensity (VEC) as a function of time.
According to the electrocardiogram presented, what was thenumber of heartbeats per minute of this patient during the exam?
a) 30
b) 60
c) 100
d) 120
e) 180
It is a wave phenomenon based on the definitions of period (T) and frequency (f) whose theory is as follows:
In the case of exercise, on an electrocardiogram the time interval between each peak corresponds to the
period (T) of a beat that is provided by the graph.
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10- (ENEM – MEC – 021)
Analyzing the technical specifications of a popular car , some characteristics can be seenin relation to its performance.
Considering the same car in two versions, one of them running on alcohol and the other ,
gasoline, you have the data presented in the table, in relation to the performance of each engine.
Considering air resistance to be negligible, which version has the greatest power?
a) As the gasoline version achieves the greatest acceleration, it is the one that develops the greatest power.
b) As the gasoline version reaches the highest kinetic energy value, it is the one that develops the greatest power.
c) As the alcohol version has the highest rate of variation in kinetic energy, it is the one that develops the greatest power.
d) As both versions present the same speed variation in the acceleration calculation, the power developed is the same.
e) As the gasoline version keeps the engine working for longer to reach 100 km/h, this is the one that develops the greatest power.
The theory used to solve the exercise is as follows:
Kinetic energy theorem
In the figure below, the car with mass m has the intensity of its speed varying from Vo to V, in a time interval ∆t:
Definition of the Kinetic Energy Theorem: “The work of the resultant of all the forces acting on a body is equal to the variation of the kinetic energy suffered by the body”
Thus, the work of the resulting force on the car of mass m in the figure above in its displacement from A to B is given by:
The above expressions are valid whether the resulting force is conservative or not.
Power (P)
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11- (ENEM – MEC – 021)
It is possible to power low-current electrical devices using common laboratory materials instead of traditional batteries.
The illustration shows an assembly that operates a digital stopwatch.
Using the representation of electrical projects , the equivalent circuit to this system is
Theory – A little chemistry
Daniell stack
The Daniell cell is made up of two electrodes: the anode (negative pole) , where zinc loses electrons, oxidizing; and the cathode (positive pole), where copper cations receive electrons and are reduced.
See the diagram below:
In the case of exercise:
Symbols:
There are two batteries correctly connected in series (positive on one and negative on the other ).
The connecting wire (red) comes out of the negative pole of the battery on the right and is connected to the timer (resistance device R) from where another wire comes out connecting it to the positive pole of the other battery (red wire).
Now notice that, coming out of the positive pole of the first battery, the voltmeter associated with the negative pole of the second battery is connected.
Both the voltmeter and the stopwatch are connected in parallel to the voltage source (two batteries).
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12- (ENEM – MEC – 021)
The figure was taken from an old computer game called Bang! Bang!
In the game , two competitors control cannons A and B , firing bullets alternately with the aim of hitting the opponent’s cannon; to do this, they assign estimated values for the module of the initial firing
and for the firing angle (θ).
At a certain point in a match, competitor B must fire; he knows that the bullet fired previously, θ = 53°, passed tangent to point P.
Available at: http://mebdownloads.butzke.net.br.
Accessed on: April 18, 2015 (adapted).
Based on the given distances and maintaining the last firing angle, what should be, approximately, the smallest value of 
that would allow the shot fired by gun B to hit gun A?
a) 30 m/s.
b) 35 m/s.
c) 40 m/s.
d) 45 m/s.
e) 50 m/s.
This is an oblique launch whose theoretical summary is presented below:
OBLIQUE LAUNCH
Decomposition of oblique movement
The oblique movement is decomposed into a movement along the horizontal direction (X axis) and another along the vertical direction (Y axis).
Equations of motion in the vertical direction
Partial movement in the horizontal direction (X axis)
(
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13- (ENEM – MEC – 021)
The wind chime is made up of several metal bars ofsame material and thickness, but different lengths, as shown in the figure.
The wind chime can be made up of open tubes or closed tubes.
Wavelengths and frequencies for a tube closed at one end
Wavelengths and frequencies for a tube open at both ends
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14- (ENEM – MEC – 021)
A 61-year-old amateur cyclist used a heart rate monitor to measure his heart rate on four different types of sections of the course.
The results of the maximum heart rates achieved in these sections were:
It is known that the ideal aerobic range for gaining physical fitness is between 65% and 85% of the maximum heart rate (F c max ) , which, in turn, is determined by the formula:
F c max. = 220 – age, where age is given in years and F c max. is given in bpm (beats per minute) .
The sections of the route in which this cyclist remains within his ideal aerobic range, for gaining physical fitness, are
a) light on the flat, strong on the flat, moderate climb and strong climb.
b) light on the flat, strong on the flat and moderate climb.
c) strong on the flat, moderate climb and strong climb.
d) strong on the flat and moderate climb.
e) light on the flat and steep climb.
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