The hot liquid cooled slowly. Why does the water flow poorly from the mixer? What to do if the hot water is lukewarm
Weak tap pressure can irritate even the most balanced homeowner. After all, the duration of filling the kettle or coffee maker and the performance of the washing or dishwasher depend on the pressure.
In addition, with poor pressure, it is almost impossible to use either the toilet, shower or bath. In a word, if there is no pressure in the tap, then there will be no comfort of living in the house.
We understand the reasons for the weak water pressure in the tap
What weakens the water pressure in the tap?
Why a weak water pressure in a tap can ruin even the happiest life even in the most perfect house or apartment, we have already discussed with you. However, groaning will not help grief. Moreover, this problem is not as bad as it seems. One has only to understand what weakened the pressure, and you will get an almost ready-made recipe for eliminating this trouble.
In this case, the list of TOP-3 reasons for a drop in the pressure of hot or cold water is as follows:
- Clogged tap ... In this case, the intensity of the water jet weakens the rust and scale plug that clogs the aerator, filter insert (mesh) or axle box. Moreover, only one tap in the house suffers from this problem. That is, if you have poor water flow from the tap, for example, in the kitchen, but there are no problems in the bathroom, then you will have to disassemble and clean the problematic point of consumption.
- ... In this case, the same particles of silt, rust or scale are to blame. Only now they are not blocking the tap aerator or the mixer mesh, but the filter built into the water supply system. In the worst case, such deposits can block the bore of the connection fitting or the pipe fitting itself.
- ... In this case, the cause of the weakening can be either a failure at the level of the pumping station, or a depressurization of the pipeline. Failure at the station can be corrected only by the repair crews of utilities. An indicator of this breakdown is the lack of water in the entire neighborhood. Loss of tightness is diagnosed visually - by the stream of water beating from the body of the plumbing fittings. Any locksmith from the service company can fix this breakdown.
- In addition, speaking about the reasons for the weakening of the pressure, it is necessary to mention and possible miscalculations when arranging a specific water supply line ... Wrong diameter (larger than that of the previous branch), excessive length (inappropriate to the characteristics of pressure equipment) are the main reasons for the drop in pressure in the new water supply network.
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If you don’t want to run into them, order a water supply project from professionals.
Well, now that you already know the reasons for the drop in pressure in the tap, it's time to figure out how to eliminate this defect in the water supply.
What to do if cold and hot water flows poorly from the tap?
It all depends on the reason for the drop in pressure.
For example, if your tap is clogged, you will have to do the following:
Remove the mixer aerator for cleaning
- Take an adjustable wrench and twist it off the "nose" of the tap - foaming water jet nozzle. This part has very small nozzles. Therefore, aerators are clogged every six months. And if we are talking about a tap mixer with hot / cold water, then the frequency of cleaning the nozzles is reduced to 2-3 months. The dismantled aerator is rinsed under running water.
- If the aerator is clean and the water is weak, you will have to dive deeper into the faucet structure ... Indeed, in this case, you need to get close to the locking unit - the axle box. To do this, you need to dismantle the valve (crane handle) and unscrew the lock washer holding the shut-off element in the body seat. Next, you remove the locking assembly from the body and clean off sludge or scale deposits from its surface. In the final, you will have to assemble the crane, following the reverse scheme.
Before dismantling the stop valve assembly, be sure to shut off the water supply by closing the water valve closest to the point of consumption. Otherwise, you will flood the whole apartment.
- If the source of the problem is not the faucet, but the "spray" in the shower or bathroom, you will have to act a little differently. Shut off the supply to the sprayer first. Then remove it from the stand or metal hose using an adjustable wrench. Dip the removed part of the spray bottle into the vinegar pot. Warm this medium on a hot plate. Rinse off limescale with water. Replace the attachment.
If the vinegar smell irritates you, try a 10% citric acid solution. For its preparation, it is enough to dissolve 100 grams of dry acid powder - it is sold in any confectionery department - in a liter of water.
If you have no desire to fiddle with a crane, call a locksmith from the management company. He will solve this problem right before your eyes.
We hope you have already understood what to do if the water pressure in the tap is poor.
Now let's move on to pipes:
- First of all, turn off the water by turning the central valve near the meter.
- Next, dismantle the coarse filter plug. Remove the wire cassette and rinse it in a container. Then put the filter element back in place, renew the seal and screw the plug.
- After revising the coarse filter, proceed to checking the fine filter system. First, disconnect it from the water supply and check the pressure in the free pipe by slightly opening the central valve. If everything is in order, change the liner, at the same time rinsing the filter bowl from particles of accumulated dirt. In the final, of course, everything is assembled in the same place.
- If the filters are clean, and the water still does not come out of the tap with the proper force, then the reason for the drop in pressure is the blockage in the pipes themselves. Localizing this problem and fixing it is an extremely time consuming task. Therefore, after the ineffective cleaning of the filters, you will have to call the management company and report the problem with the passage of pipes in the water supply.
If you have not changed the wiring of the water supply system in the apartment, the management company will pay for the cleaning of the pipes. After all, it is she who must monitor the performance of "native" engineering communications.
228. In the electric kettle, the faulty heater was replaced with a heater with twice the power. The boiling point of water is
229. The hot liquid cooled slowly in a glass. The table shows the results of measurements of its temperature over time.
In the glass, 7 min after the start of measurements, there was a substance
230. To melt a piece of tin, already heated to its melting point, requires 1.8 kJ of energy. This piece was put into the oven. The dependence of the tin temperature on the heating time is shown in the figure. How fast did the oven transfer heat to the tin?
232. The figure shows graphs of the temperature variation of four substances with time. At the beginning of heating, all these substances were in a liquid state. Which substance has the highest boiling point?
234. At the initial moment of time, the substance was in a crystalline state. The figure shows a graph of its temperature T versus time t. Which point corresponds to the end of the curing process?
| 1) | 2) | 3) | 4) |
235. (B). To determine the specific heat of fusion, pieces of melting ice were thrown into a vessel with water weighing 300 g and a temperature of 20 ° C with continuous stirring. By the time the ice stopped melting, the mass of water increased by 84 g. Determine the specific heat of melting from the experiment data. Express your answer in kJ / kg.
236. (B).Into a heat-insulated vessel with a lot of ice at a temperature t 1 \u003d 0 ° C fill m\u003d 1 kg of water with a temperature t 2 \u003d 44 ° C. What is the mass of ice D m melt when thermal equilibrium is established in the vessel? Express your answer in grams.
237. (B). A tube is lowered into a vessel with water. Steam is passed through the tube at a temperature of 100 ° C. Initially, the mass of water increases, but at some point, the mass of water stops increasing, although steam is still passed through. The initial mass of water is 230 g, and at the end it is 272 g. What is the initial temperature of the water on the Celsius scale? Neglect the loss of heat.
238. (C). The calorimeter contained 1 kg of ice. What was the temperature of the ice if, after adding 15 g of water at a temperature of 20 ° С to the calorimeter, thermal equilibrium was established in the calorimeter at - 2 ° С? The heat exchange with the environment and the heat capacity of the calorimeter should be neglected.
Unified State Exam in Physics, 2009,
demo version
Part A
A1. The figure shows a graph of the dependence of the projection of the body's velocity on time. The graph of the dependence of the projection of the acceleration of the body on time in the time interval from 12 to 16 s coincides with the graph
| 1) |
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| 2) |
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| 3) |
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| 4) |
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Decision. The graph shows that in the time interval from 12 to 16 s, the speed varied uniformly from –10 m / s to 0 m / s. The acceleration was constant and equal
The acceleration graph is shown in the fourth figure.
Correct answer: 4.
A2. Strip magnet mass m brought to a massive steel plate with a mass M... Compare the force of the magnet on the cooker with the force of the slab on the magnet.
| 1) | |
| 2) | |
| 3) | |
| 4) |
Decision. According to Newton's third law, the force with which the magnet acts on the plate is equal to the force with which the plate acts on the magnet.
Correct answer: 1.
A3. When moving on a horizontal surface, a sliding friction force of 10 N acts on a body weighing 40 kg. What will be the sliding friction force after a 5-fold decrease in body mass, if the coefficient of friction does not change?
| 1) | 1 N |
| 2) | 2 H |
| 3) | 4 N |
| 4) | 8 N |
Decision. With a decrease in body weight by 5 times, body weight will also decrease by 5 times. This means that the sliding friction force will decrease by a factor of 5 and amount to 2 N.
Correct answer: 2.
A4. A car and a truck are moving at speeds 
and. Passenger car weight m \u003d 1000 kg. What is the mass of a truck if the ratio of the momentum of the truck to the momentum of a passenger car is 1.5?
| 1) | 3000 kg |
| 2) | 4500 kg |
| 3) | 1500 kg |
| 4) | 1000 kg |
Decision. The momentum of the car is equal. Truck momentum is 1.5 times greater. The mass of the truck is equal.
Correct answer: 1.
A5. Sledge weight m pulling uphill at a constant speed. When the sleigh rises to the top h from the initial position, their total mechanical energy
Decision. Since the sled is pulled at a constant speed, its kinetic energy does not change. The change in the total mechanical energy of the sled is equal to the change in their potential energy. The total mechanical energy will increase by mgh.
Correct answer: 2.
| 1) | 1 |
| 2) | 2 |
| 3) | |
| 4) | 4 |
Decision. The wavelength ratio is inversely proportional to the frequency ratio:.
Correct answer: 4.
A7. The photograph shows a setup for studying uniformly accelerated sliding of a carriage (1) weighing 0.1 kg along an inclined plane set at an angle of 30 ° to the horizon.
At the moment of the start of movement, the upper sensor (A) turns on the stopwatch (2), and when the carriage passes the lower sensor (B), the stopwatch turns off. The numbers on the ruler represent the length in centimeters. Which expression describes the time dependence of the carriage speed? (All values \u200b\u200bare in SI units.)
| 1) | |
| 2) | |
| 3) | |
| 4) |
Decision. The figure shows that over time t \u003d 0.4 s the carriage has traveled a path s \u003d 0.1 m.Since the initial speed of the carriage is zero, you can determine its acceleration:
.
Thus, the speed of the carriage depends on time according to the law.
Correct answer: 1.
A8. With a decrease in the absolute temperature of a monatomic ideal gas by 1.5 times, the average kinetic energy of the thermal motion of its molecules
Decision. The average kinetic energy of the thermal motion of ideal gas molecules is directly proportional to the absolute temperature. With a decrease in the absolute temperature by 1.5 times, the average kinetic energy will also decrease by 1.5 times.
Correct answer: 2.
A9. The hot liquid cooled slowly in a glass. The table shows the results of measurements of its temperature over time.
In the glass, 7 min after the start of measurements, there was a substance
Decision. The table shows that between the sixth and tenth minutes, the temperature in the glass remained constant. This means that crystallization (solidification) of the liquid took place at this time; the substance in the glass was simultaneously in liquid and solid states.
Correct answer: 3.
A10. What work does the gas do during the transition from state 1 to state 3 (see figure)?
| 1) | 10 kj |
| 2) | 20 kj |
| 3) | 30 kj |
| 4) | 40 kj |
Decision. Process 1–2 is isobaric: the gas pressure is equal, the volume increases by, while the gas does work. Process 2–3 is isochoric: the gas does not perform work. As a result, during the transition from state 1 to state 3, the gas performs work of 10 kJ.
Correct answer: 1.
A11. In a heat engine, the temperature of the heater is 600 K, the temperature of the refrigerator is 200 K less than that of the heater. The maximum possible efficiency of the machine is
| 1) | |
| 2) | |
| 3) | |
| 4) |
Decision. The maximum possible efficiency of a heat engine is equal to the efficiency of a Carnot machine:
.
Correct answer: 4.
A12. The vessel contains a constant amount of ideal gas. How will the gas temperature change if it goes from state 1 to state 2 (see figure)?
| 1) | |
| 2) | |
| 3) | |
| 4) |
Decision. According to the equation of state of an ideal gas at a constant amount of gas
Correct answer: 1.
A13. The distance between two point electric charges was reduced by 3 times, and one of the charges was increased by 3 times. The forces of interaction between them
Decision. When the distance between two point electric charges decreases by 3 times, the force of interaction between them increases by 9 times. An increase in one of the charges by 3 times leads to the same increase in strength. As a result, the strength of their interaction became 27 times greater.
Correct answer: 4.
A14. What will be the resistance of the circuit section (see figure) if the key K is closed? (Each of the resistors has a resistance R.)
| 1) | R |
| 2) | 2R |
| 3) | 3R |
| 4) | 0 |
Decision. After the key is closed, the terminals will be shorted, the resistance of this section of the circuit will become zero.
Correct answer: 4.
A15. The figure shows a wire loop through which an electric current flows in the direction indicated by the arrow. The coil is located in the vertical plane. In the center of the loop, the induction vector of the magnetic field of the current is directed
Decision. According to the rule of the right hand: "If you grasp the solenoid (coil with current) with the palm of your right hand so that four fingers are directed along the current in the coils, then the left thumb will show the direction of the magnetic field lines inside the solenoid (coil with current)." Having done the indicated actions mentally, we find that in the center of the loop the magnetic induction vector is directed horizontally to the right.
Correct answer: 3.
A16. The figure shows a graph of harmonic current fluctuations in the oscillatory circuit. If the coil in this circuit is replaced with another coil, the inductance of which is 4 times less, then the oscillation period will become equal to
| 1) | 1 μs |
| 2) | 2 μs |
| 3) | 4 μs |
| 4) | 8 μs |
Decision. The graph shows that the period of current fluctuations in the oscillatory circuit is 4 μs. When the inductance of the coil is reduced by 4 times, the period will decrease by 2 times. After replacing the coil, it will become equal to 2 μs.
Correct answer: 2.
A17. Light source S is reflected in a flat mirror ab... The image S of this source in the mirror is shown in the figure
Decision. The image of the object, obtained using a flat mirror, is located symmetrically to the object relative to the plane of the mirror. The image of the source S in the mirror is shown in Figure 3.
Correct answer: 3.
A18. In a certain spectral range, the angle of refraction of the rays at the air-glass interface decreases with increasing radiation frequency. The path of rays for the three primary colors when white light falls from air to the interface is shown in the figure. The numbers correspond to the colors
Decision. Due to the dispersion of light, when passing from air to glass, the beam deviates more from its original direction, the shorter its wavelength. Blue has the shortest wavelength, red has the longest. The blue ray will deflect the most (1 - blue), the red ray will deflect the least (3 - red), 2 remains green.
Correct answer: 4.
A19. At the entrance to the electrical circuit of the apartment there is a fuse that opens the circuit at a current of 10 A. The voltage supplied to the circuit is 110 V. What is the maximum number of electric kettles, each of which is 400 W, can be turned on at the same time in an apartment?
| 1) | 2,7 |
| 2) | 2 |
| 3) | 3 |
| 4) | 2,8 |
Decision. An electric current with a power of 400 W passes through each kettle: 110 V 3.64 A. When two kettles are turned on, the total current strength (2 3.64 A \u003d 7.28 A) will be less than 10 A, and when three kettles are turned on, more 10 A (3 3.64 A \u003d 10.92 A). No more than two kettles can be switched on at the same time.
Correct answer: 2.
A20. The figure shows diagrams of four atoms corresponding to Rutherford's model of the atom. Black dots indicate electrons. The scheme corresponds to the atom
| 1) |
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| 2) | |
| 3) |
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| 4) |
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Decision. The number of electrons in a neutral atom coincides with the number of protons, which is written at the bottom before the name of the element. An atom has 4 electrons.
Correct answer: 1.
A21. The half-life of the nuclei of radium atoms is 1620 years. This means that in a sample containing a large number of radium atoms,
Decision. It is true that half of the original radium nuclei decay in 1620 years.
Correct answer: 3.
A22. Radioactive lead, having experienced one α-decay and two β-decays, turned into an isotope
Decision. During α decay, the mass of the nucleus decreases by 4 amu. e. m., and during β-decay the mass does not change. After one α-decay and two β-decays, the mass of the nucleus will decrease by 4 amu. eat.
During α-decay, the nuclear charge decreases by 2 elementary charges, and during β-decay, the charge increases by 1 elementary charge. After one α-decay and two β-decays, the nuclear charge will not change.
As a result, it will turn into a lead isotope.
Correct answer: 3.
A23. The photoelectric effect is observed by illuminating the metal surface with light of a fixed frequency. In this case, the retarding potential difference is U... After changing the frequency of the light, the retarding potential difference increased by Δ U \u003d 1.2 V. How much has the incident light frequency changed?
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Decision. Let us write down the Einstein equation for the photoelectric effect for the initial frequency of light and for the changed frequency. Subtracting the first equality from the second, we get the ratio:
Correct answer: 2.
A24. The conductors are made from the same material. Which pair of conductors should be chosen in order to experimentally discover the dependence of the resistance of the wire on its diameter?
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| 2) |
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| 3) |
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| 4) |
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Decision. In order to experimentally discover the dependence of the resistance of the wire on its diameter, you need to take a pair of conductors that differ only thick. The length of the conductors must be the same. You need to take the third pair of conductors.
Correct answer: 3.
A25. The dependence of the voltage across the plates of an air capacitor on the charge of this capacitor was investigated. The measurement results are presented in the table.
Measurement errors q and U were equal to 0.05 μC and 0.25 kV, respectively. The capacitance of the capacitor is approximately equal
| 1) | 250 pF |
| 2) | 10 nF |
| 3) | 100 pF |
| 4) | 750 uF |
Decision. We calculate for each measurement the value of the capacitance of the capacitor () and average the resulting values.
| q, μC | 0 | 0,1 | 0,2 | 0,3 | 0,4 | 0,5 | |
| U, kV | 0 | 0,5 | 1,5 | 3,0 | 3,5 | 3,5 | |
| FROM, pF | - | 200 | 133 | 100 | 114 | 142 | 140 |
The calculated capacity value is closest to the third answer.
Correct answer: 3.
Part B
IN 1. Mass weight m, suspended on a spring, performs harmonic oscillations with a period T and amplitude. What happens with the maximum potential energy of the spring, the period and frequency of oscillations, if the weight of the load is reduced at a constant amplitude?
For each position of the first column, select the corresponding position of the second and write down the selected numbers in the table under the corresponding letters.
| AND | B | IN |
Transfer the resulting sequence of numbers to the answer form (without spaces).
Decision. The period of vibration is related to the mass of the load and the stiffness of the spring. k ratio
With a decrease in mass, the period of oscillations will decrease (A - 2). The frequency is inversely proportional to the period, which means that the frequency will increase (B - 1). The maximum potential energy of the spring is equal, with a constant vibration amplitude, it will not change (B - 3).
Answer: 213.
AT 2. Using the first law of thermodynamics, establish a correspondence between the features of the isoprocess in an ideal gas described in the first column and its name.
| AND | B |
Transfer the resulting sequence of numbers to the answer form (without spaces and any symbols).
Decision. The internal energy of an ideal gas remains unchanged at a constant gas temperature, that is, in an isothermal process (A - 1). Heat exchange with surrounding bodies is absent in the adiabatic process (B - 4).
AT 3. A flying projectile explodes into two fragments. In relation to the direction of movement of the projectile, the first fragment flies at an angle of 90 ° at a speed of 50 m / s, and the second at an angle of 30 ° at a speed of 100 m / s. Find the ratio of the mass of the first fragment to the mass of the second fragment.
R solution. Let's depict the directions of movement of the projectile and two fragments (see figure). Let us write the law of conservation of the projection of the momentum on the axis perpendicular to the direction of movement of the projectile:
AT 4. In a heat-insulated vessel with a large amount of ice at a temperature, pour m \u003d 1 kg of water with temperature. What is the mass of ice Δ m melt when thermal equilibrium is established in the vessel? Express your answer in grams.
Decision. When cooled, the water will give up the amount of heat. This warmth will melt the ice in bulk
Answer: 560.
AT 5. An object 6 cm high is located on the main optical axis of a thin collecting lens at a distance of 30 cm from its optical center. The optical power of the lens is 5 diopters. Find the height of the subject image. Express your answer in centimeters (cm).
Decision. Let's denote the height of the object h \u003d 6 cm, distance from the lens to the object, the optical power of the lens D \u003d 5 diopters. Using the formula for a thin lens, we determine the position of the image of the object:
.
The increase will be
.
Image height is
Part C
C1. A man with glasses walked into a warm room from the street and found that his glasses were fogged up. What should be the temperature outside for this phenomenon to be observed? In the room the air temperature is 22 ° C, and the relative humidity is 50%. Explain how you got your answer.
(When answering this question, use the water vapor pressure table.)
Pressure of saturated water vapor at different temperatures
Decision. From the table we find that the saturated vapor pressure in the room is 2.64 kPa. Since the relative humidity is 50%, the partial pressure of water vapor in the room is 2.164 kPa 50% \u003d 1.32 kPa.
At the first moment, as a person entered from the street, his glasses have a street temperature. Room air, in contact with the glasses, is cooled. The table shows that if the room air cools down to 11 ° C or lower, when the partial pressure of water vapor becomes greater than the pressure of saturated vapor, water vapor condenses - the glasses will fog up. The temperature outside should be no higher than 11 ° C.
Answer: not higher than 11 ° C.
C2. The small puck after impact slides up the ramp from the point AND (see figure). At the point IN an inclined plane without a break goes into the outer surface of a horizontal pipe with a radius R... If at the point AND the puck speed exceeds, then at the point IN the washer comes loose from the support. Inclined plane length AB = L \u003d 1 m, angle α \u003d 30 °. The coefficient of friction between the inclined plane and the washer μ \u003d 0.2. Find the outer radius of the pipe R.
Decision. Find the puck speed at the point Busing the law of conservation of energy. The change in the total mechanical energy of the washer is equal to the work of the friction force:
The separation condition is the equality of the support reaction force to zero. The centripetal acceleration is caused only by the force of gravity, while for the minimum initial speed for which the separation of the washer is observed, the radius of curvature of the trajectory at the point B is equal R (for higher speeds, the radius will be larger):
Answer: 0.3 m.
C3. A balloon whose shell has a mass M \u003d 145 kg and volume, filled with hot air at normal atmospheric pressure and ambient temperature. What is the minimum temperature t must there be air inside the shell for the balloon to start rising? The shell of the ball is inextensible and has a small hole in the lower part.
Decision. The ball will begin to rise when the force of Archimedes exceeds the force of gravity. Archimedes' strength is equal. The density of the outside air is
where p - normal atmospheric pressure, μ - molar mass of air, R - gas constant, - outside air temperature.
The mass of the ball is made up of the mass of the shell and the mass of air inside the shell. Gravity is
where T - the temperature of the air inside the shell.
Solving the inequality, we find the minimum temperature T:
The minimum air temperature inside the enclosure should be 539 K or 266 ° C.
Answer: 266 ° C.
C4. A thin rectangular aluminum bar with a length L \u003d 0.5 m, slides from a state of rest along a smooth inclined plane from a dielectric in a vertical magnetic field with induction B \u003d 0.1 T (see figure). The plane is inclined to the horizon at an angle α \u003d 30 °. The longitudinal axis of the bar remains horizontal during movement. Find the value of the EMF induction at the ends of the bar at the moment when the bar passes the distance along the inclined plane l \u003d 1.6 m.
Decision. Find the speed of the bar in the lower position using the energy conservation law:
Aluminum is a conductor, so an induction EMF will appear in the bar. EMF of induction at the ends of the bar will be equal to
Answer: 0.17 V.
C5. In the electrical circuit shown in the figure, the EMF of the current source is 12 V, the capacitance of the capacitor is 2 mF, the inductance of the coil is 5 mH, the resistance of the lamp is 5 Ohm and the resistance of the resistor is 3 Ohm. At the initial moment of time, the key K is closed. What energy will be released in the lamp after opening the key? The internal resistance of the current source, as well as the resistance of the coil and wires, should be neglected.
Decision. Let's introduce the designations: ε - EMF of the current source, C - capacity of the capacitor, L - coil inductance, r - lamp resistance, R is the resistance of the resistor.
While the key is closed through the capacitor and the lamp, no current flows, but current flows through the resistor and the coil
The energy of the capacitor - lamp - coil - resistor system is
.
After opening the key, transients will occur in the system until the capacitor is discharged and the current becomes zero. All energy is released as heat in the lamp and resistor. At each moment of time, amounts of heat are released in the lamp, and in the resistor -. Since the same current will flow through the lamp and the resistor, the ratio of the generated heat will be in proportion to the resistances. Thus, energy will be released in the lamp.
Answer: 0.115 J.
C6. -meson with mass decays into two γ-quanta. Find the modulus of momentum of one of the generated γ-quanta in the reference frame where the primary -meson is at rest.
Decision. In the frame of reference where the primary -meson is at rest, its momentum is zero, and its energy is equal to the rest energy. According to the law of conservation of momentum, γ quanta will fly out in opposite directions with the same momentum. This means that the energies of γ-quanta are the same and, therefore, equal to half the energy of the -meson:. Then the momentum of the γ quantum is
Part 1
A1. The figure shows a graph of the dependence of the projection of the body's velocity on time.
The projection of the body's acceleration in the time interval from 12 to 16 s is shown in the graph:
A2. Strip magnet mass m brought to a massive steel plate with a mass M... Compare the strength of a magnet on a stove F 1 with the force of action of the plate on the magnet F 2 .
1) F 1 = F 2 ; 2) F 1 > F 2 ; 3) F 1 < F 2 ; 4) F 1 / F 2 = m / M.
A3. When moving on a horizontal surface, a sliding friction force of 10 N acts on a body weighing 40 kg. What will be the sliding friction force after a 5-fold decrease in body mass, if the coefficient of friction does not change?
1) 1 H; 2) 2 H; 3) 4 H; 4) 8 N.
A4. A car and a truck are moving at speeds υ 1 \u003d 108 km / h and υ 2 \u003d 54 km / h. Passenger car weight m \u003d 1000 kg. What is the mass of a truck if the ratio of the momentum of the truck to the momentum of a passenger car is 1.5?
1) 3000 kg; 2) 4500 kg; 3) 1500 kg; 4) 1000 kg.
A5. Sledge weight m pulling uphill at a constant speed. When the sled rises to the top h from the initial position, their total mechanical energy:
1) will not change;
2) will increase by mgh;
3) will be unknown, because the slope of the slide is not set;
4) will be unknown, because coefficient of friction not specified.
1) 1; 2) 2; 3) 1/4; 4) 4.
On the FIPI website http://www.fipi.ru. For instructions on how to complete the work of the Unified State Exam-2009, the criteria for evaluating the solutions of tasks, part 3 by 1 and 2 points, the conditions for recording the solution of tasks, as well as another option, see No. - Ed.