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How to calculate 13.73-5.28 + 4.27-4.27
13.73-5.28+4.27-4.27
=13.73-5.30+0.02+（4.27-4.27）
=13.73+0.02-5.30
=13.75-5.30
=8.45
The key point is + 4.27-4.27, which offsets each other and becomes 0; 13.73-5.28 is not very important, which can be calculated simply or not
Is nuclear power generation chemical or physical?
Nuclear power generation is to generate energy for nuclear fission chain reaction, which is a physical reaction. Other types of power reactors are all primary coolant, which is heated by the reactor core. In the steam generator, heat is transferred to the secondary or tertiary water, and then steam is formed to drive the turbine generator
A practical problem about the fractional equation 150x = 150 − X2X + 2 is worked out in connection with practice. It requires complete expression, sufficient conditions and no solution
A factory needs to produce a batch of 150 parts. First, Party A will do it alone for one day, and the rest will be done by Party B. the time taken by Party B is two days less than the time taken by Party A to finish 150 parts alone. It is known that the work efficiency of Party B is twice that of Party A. how many parts does Party A do every day?
The powerful power generated by the Three Gorges hydropower station is transformed from water energy,
The meaning is right. The sentence is not sick
If we consider from physics, that's not right. It should be derived from the kinetic energy of water flow, or the potential energy upstream
A very urgent math problem,
4.8:3.6 = 1.2: x 2. The formula for the positive proportion of X and Y is a.5xy = 26, b.y = 0.6x, c.3x + 12 = 18
1、x=3.6*1.2/4.8=0.9
2、B
I wish you a happy study!
How many jin is 1000 calories
One pound of fat is 3500 calories, and one kilogram is 2.2 pounds. So one kilogram of fat is 7716 calories
1 pound of fat = 3600 calories
1 kg fat = 7716 calories
Given that a ^ 2-6a + 9 and | B-1 | are opposite to each other, the value of formula (2a + b) / (a + b) is obtained
∵ a ^ 2-6a + 9 and | B-1 | are opposite numbers,
∴a^2-6a+9+|b-1|＝0
That is: (A-3) &# 178; + | B-1 | = 0
∴(a-3)²=0,|b-1|=0
a-3=0,b-1=0
The solution is: a = 3, B = 1
∴(2a+b)/(a+b)
=(6+1)/(3+1)
=7/4
What is the resistance of a superconductor?
Generally, when the temperature of a material is close to absolute zero, the molecular thermal motion of the object almost disappears, and the resistance of the material approaches zero. At this time, it is called a superconductor, and the temperature at which superconductivity is reached is called a critical temperature
The resistance can be considered as 0
When an object is moving in a straight line with uniform acceleration, the initial velocity is 0.5m/s, and the displacement in the 7th s is 4m more than that in the 5th s, the following results can be obtained: (1) the acceleration of the object; (2) the displacement of the object in the 5th s
(1) Using the formula of displacement difference in adjacent equal time: △ x = at2, it is obtained that: a = X7 − x52t2 = 42 = 2m / S2 (2) the displacement of the object in 5S is: x = v0t + 12at2 = 0.5 × 5 + 12 × 2 × 25 = 27.5m A: (1) the acceleration of the object is 2m / S2; (2) the displacement of the object in 5S is 27.5m
All the formulas and international units needed to master in junior high school physics
Name a few commonly used, including what density ah, moving pulley ah
Deformation of remark formula of physical quantity (unit) formula
Speed V (M / s) v = s: distance / T: time
Gravity g (n) g = mg m: mass G: 9.8n/kg or 10N / kg
Density ρ (kg / m3) ρ = m / V M: mass V: Volume
The direction of resultant force F (n) is the same: F = F1 + F2
Opposite direction: F = f 1-f 2 when the direction is opposite, F 1 > F 2
Buoyancy f
(N) F floating = g object - G view g view: gravity of object in liquid
Buoyancy f
(N) F = g, this formula is only applicable
Floating or levitating objects
Buoyancy f
(N) F floating = g row = m row, g = ρ liquid, GV row, g row: the gravity of the liquid
M row: the mass of liquid in row
ρ liquid: density of liquid
V row: volume of liquid to be discharged
(volume immersed in liquid)
Balance condition of lever f1l1 = f2l2 F1: power L1: power arm
F2: resistance L2: resistance arm
Fixed pulley f = g
S = H F: the tension on the free end of the rope
G object: the gravity of an object
S: The distance that the free end of the rope moves
h: The distance an object rises
Moving pulley f = (g object + G wheel)
S = 2 h g object: the gravity of the object
Wheel G: gravity of moving pulley
Pulley block f = (g object + G wheel)
S = N H N: the number of segments of the rope passing through the movable pulley
Mechanical work W
(J) W = FS F: force
s: The distance moved in the direction of the force
Useful work
Total work w total w = g matter H
Wtotal = FS, when the pulley block is placed vertically
Mechanical efficiency η = × 100%
Power p
（w） P=
W: Merit
t: Time
Pressure P
（Pa） P=
F: Pressure
S: Stress area
Liquid pressure P
(PA) P = ρ GH ρ: density of liquid
h: Depth (from liquid level to desired point)
The vertical distance of the
Heat Q
(J) Q = cm △ T C: specific heat capacity m: mass
Δ T: change value of temperature
Fuel emission
Q (J) q = MQ M: mass
q: Calorific value
Common physical formulas and important knowledge points
1、 Physical formula
Unit) formula remarks formula deformation
Series circuit
Current I (a) I = I1 = I2 = The current is equal everywhere
Series circuit
Voltage U (V) u = U1 + U2 + Start of series circuit
Partial pressure action
Series circuit
Resistance R (Ω) r = R1 + R2 +
Parallel circuit
Current I (a) I = I1 + I2 + The main circuit current is equal to the current of each circuit
Sum of branch currents (shunt)
Parallel circuit
Voltage U (V) u = U1 = U2 =
Parallel circuit
Resistance R (Ω) = +
Ohm's law I=
Current and voltage in circuit
In direct proportion to the resistance
Current definition I=
Q: Charge quantity (Coulomb)
t: Time (s)
Electric work W
(J) W = uit = Pt U: voltage I: current
t: Time p: electric power
Electric power P = UI = I2R = U2 / r u: voltage I: current
R: Resistance
Electromagnetic wave velocity and wave propagation
The relationship between length and frequency C = λ ν C: wave velocity (the wave velocity of electromagnetic wave is constant, equal to 3 × 108m / s)
λ: Wavelength V: frequency
2、 Knowledge points
1. Several values to remember:
a. Sound propagation speed in air: 340m / S B light propagation speed in vacuum or air: 3 × 108m / S
c. The density of water is 1.0 × 103kg / m3 D. the specific heat capacity of water is 4.2 × 103J / (kg ᦇ 8226; ℃)
e. Voltage of a dry battery: 1.5V F. voltage of household circuit: 220V
g. Safety voltage: not higher than 36V
2. Density, specific heat capacity and calorific value are the characteristics of a substance. The values of the three physical quantities of the same substance generally do not change. For example, a cup of water and a bucket of water have the same density and specific heat capacity,
3. A virtual image of equal size formed by a plane mirror. The image and the object are symmetrical about the plane mirror
3. Sound cannot be transmitted in vacuum, but light can be transmitted in vacuum
4. Ultrasound: sound with frequency higher than 20000 Hz, e.g. bat, ultrasonic radar;
5. Infrasound: volcanic eruption, earthquake, wind explosion, tsunami can produce infrasound, nuclear explosion, missile launch can also produce infrasound
6. Light propagates along a straight line in the same homogeneous medium. Shadow, pinhole imaging, solar eclipse and lunar eclipse are all formed by light propagating along a straight line
7. When light is refracted, the angle in the air is always a little larger. When you look at the objects in the water, you can see a shallow virtual image
8. Convex lens converges and concave lens diverges
9. The law of convex lens imaging: the object forms a reduced and inverted real image outside the double focal length. Between the double focal length and the double focal length, the object forms an inverted and enlarged real image. Within the double focal length, the object forms an upright and enlarged virtual image
Sliding friction is related to pressure and surface roughness. Rolling friction is smaller than sliding friction
11. Pressure is a physical quantity to compare the effect of pressure. The effect of pressure is related to the size of pressure and the stressed area
12. When transmitting voltage, high voltage should be used to transmit electricity. The reason is that the loss of electric energy on the transmission line can be reduced
13. The principle of motor: the electrified coil rotates under the force in the magnetic field. It is the conversion of electric energy into mechanical energy
Principle of generator: electromagnetic induction phenomenon. Mechanical energy is converted into electric energy. Microphone and transformer use the principle of electromagnetic induction
15. Optical fiber is the medium for transmitting light
16. The magnetic induction line comes from the N pole of the magnet and finally returns to the S pole
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