Xiao Li borrowed a book from the library. It has 132 pages in total. After reading it for five days, there are 72 pages left. How many pages do you need to read every day on average? If you can only borrow it for nine days, how many pages do you need to read from the sixth day

Xiao Li borrowed a book from the library. It has 132 pages in total. After reading it for five days, there are 72 pages left. How many pages do you need to read every day on average? If you can only borrow it for nine days, how many pages do you need to read from the sixth day

Xiao Li borrowed a copy of space exploration from the library
 

Xiao Li borrowed 132 pages of space exploration notes from her library. After five days, it was 72 pages. How many pages did she read every day

（132-72）÷5
=60÷5
=12 pages
Average 12 pages per day

What happens when two lamps marked with 220 V 40 W and 220 V 100 W are connected in series to the 440 V circuit

Total resistance 1210 + 484 = 1694 Ω
Current = 440 △ 1694 = 0.26A
The power of 220 V 40 W bulb is 0.26 & sup2; × 1210 = 81.6 W
The 220 V 40 W bulb will be burned

Three fifths minus three fifths divided by three plus six fifths is a simple calculation

=3 out of 5 minus 3 out of 5 times 1 out of 3 plus 6 out of 25
=3 / 5 minus 1 / 5 plus 6 / 25
=2 out of 5 plus 6 out of 25
=10 out of 25 plus 6 out of 25
=16 out of 25

The coil resistance of a motor is 1 ohm, which is connected in a 220 V circuit. The current of the motor is 2.5 a. the current does work in 1 min? The heat generated by the current passing through the coil?

This is not a pure resistance circuit, and Joule's law cannot be used
The work done by current is the total work: w = IUT = 2.5 * 220 * 60 = self calculation
The heat generated by the current through the coil is the thermal power, which can be calculated by Joule's Law: w = I ^ 2 (square) rt = (220 / 1) ^ 2 * 1 * 60 = self

Simple calculation of 7.25 times 99 plus 7.25

=7.25*(99+1) =7.25*100 =725

How many joules of heat can be released by burning one kilogram of coal, please

29260000 joules

Solving fractional equation! 80 / x = 100 / x + 2

The first step is 80 = 100 + 2x
Step 2 2x = - 20
Step 3 x = - 10
The fourth step is to check whether it meets the meaning of the question
Step 5 x = - 10

Wind turbine is a device that converts wind energy (kinetic energy of air flow) into electrical energy. Its main components include wind turbine, gearbox, generator, etc. (as shown in the figure). When wind power is generated, the blades of wind turbine rotate after being pushed by the wind, thus driving the generator to generate electricity, When the wind speed is 8 m / s, the air mass flowing to the blade rotation area per second is 7 200 kg, and the air density is 1.2 kg / m3; It is known that the air kinetic energy is directly proportional to the air mass, and the kinetic energy (E) of 1kg air at different speeds (V) is shown in the following table. E (J) 28183250 V (M / s) 246810 (1) when the wind speed is 8m / s, what is the volume of air passing through the blade rotation area per second? If the calorific value of coal is 3.2 × 107 J / kg, then the wind energy obtained by such a wind turbine in one hour is equivalent to the internal energy generated by the complete combustion of how many kilograms of coal? (2) When the wind speed is 10 m / s, what is the mass of air flowing to the blade rotating area in 1 s? In this case, if the wind turbine can provide 5.4 × 104j of electric energy, then what is the efficiency of the wind energy into electric energy of the wind turbine? (3) Scientists believe that the ideal air power plant should be built at an altitude of 4600m to 10000m. Why?

(1) According to ρ = MV, v = m, ρ = 7200kg, 1.2kg/m3 = 6000m3, the energy produced by air in one hour is q = 32j / kg × 7200kg / s × 3600s = 8.2944 × 108j, the wind energy obtained in one hour is quite complete combustion of coal: M = QQ = 8.2944 × 108j3.2 × 107j / kg = 25.92kg. (2) suppose that the rotating area of the fan blade is s, the wind speed is V, the air flow through the fan in unit time t is v = SL = s · VT, then the air flow through the fan is v The mass of air is: M = ρ v = ρ s · VT; when the air density, the rotating area of the fan blade and the time are the same, m and V are proportional; that is: m ′ V ′ = MV, m ′ = MV ′ v = 7200kg, 8m / s × 10m / S = 9000kg. According to the table, the energy generated is: e wind = 50J / kg × 9000kg = 4.5 × 105J, and the efficiency of wind energy conversion into electric energy of this wind turbine is: η = e wind × 100% = 5.4 × 104j4 5 × 105J × 100% = 12%. & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; (3) because the higher the altitude is, the higher the air flow velocity is, the more energy is generated, so as to improve the conversion efficiency of wind turbine, so the ideal air power plant should be built in the air with an altitude of 4600m to 10000m