On the number axis, O is the origin, a and B are - 8 and 2, respectively 1. Finding the length of ab 2. The moving point P starts from a and moves to the right along the number axis with a speed of 3 unit lengths per second; meanwhile, the moving point Q starts from B and moves to the left along the number axis with a speed of 1 unit length per second. When P and Q coincide, the two points stop moving at the same time. Let the movement time of the two points be T seconds, and a formula containing t be used to express the length of the segment PQ 3. Under the condition of (2), the distance from point P and Q to origin o is equal when t is the value And do timely explanation, the more detailed the better, 3Q~

On the number axis, O is the origin, a and B are - 8 and 2, respectively 1. Finding the length of ab 2. The moving point P starts from a and moves to the right along the number axis with a speed of 3 unit lengths per second; meanwhile, the moving point Q starts from B and moves to the left along the number axis with a speed of 1 unit length per second. When P and Q coincide, the two points stop moving at the same time. Let the movement time of the two points be T seconds, and a formula containing t be used to express the length of the segment PQ 3. Under the condition of (2), the distance from point P and Q to origin o is equal when t is the value And do timely explanation, the more detailed the better, 3Q~

1、AB=|-8-2|=10
2. After T seconds, the corresponding position of P is: - 8 + 3T; the corresponding position of Q is: 2-t
Therefore, PQ = | - 8 + 3T) - (2-T) | = | 4t-10|
When two points overlap, the time required is 10 / 4 = 2.5 seconds
Therefore, the movement time is 0 ≤ t ≤ 2.5
Therefore, PQ = 10-4t
3. According to ②, Po = | 3t-8 | and Qo = | 2-t|
When Po = Qo, there is: | 3t-8 | = | 2-t|
===> |3t-8|=|t-2|
===>3t-8 = T-2, or 3t-8 = 2-T
===>2T = 6, or 4T = 10
===>T = 3, or T = 2.5
And 0 ≤ t ≤ 2.5
So, t = 2.5
10；PQ=10-4t（0
It is known that on the number axis, points a and B represent rational numbers a and B respectively, and the origin is just the midpoint of AB, then 2008 * B / A=
a. B is opposite to each other, a = - B, B = - A
2008×a/b = 2008×a/(-a)=-2008
-2008 because the origin is the midpoint, a = - B can be substituted
2008*b/a=-2008
-2008
On the number axis, points a and B represent rational numbers a and B respectively, and the origin o is just the midpoint of line ab. what is the value of 2004a × 26 / 3B?
26 / 3B means 26 out of 3B
∵a=-b,∴a/b=-1
∴2004a*26/3b=-2004*26/3=-17368
a=-b.
2004a×26/3b=-2004×26/3=-668×26=-17368
Junior high school physics formula and the meaning and unit of each letter
Summary of junior high school physics concepts
Physical quantity name physical quantity symbol unit name unit symbol formula
ρ M = kg mass
Temperature T ° C ° C
Velocity v m / S M / S v = s / T
Density p kg / M & sup3; kg / M & sup3; P = m / V
Force (gravity) f Newton (cow) n g = mg
Pressure P Pascal PA P = f / S
Work w Joule (joule) J W = FS
Power P watt W P = w / T
Current I a (a) a i = u / R
Voltage U V U = IR
Resistance R ohm (Ω) r = u / I
Electric work w Joule (joule) J W = UI t
Electric power P watt (watt) W P = w / T = UI
Heat Q Joule (joule) J Q = cm △ t
Specific heat C coke per kilogram degree centigrade J / (kg &; ° C) C = q / m △ t
Common data:
The speed of light in vacuum is 3 × 10 ^ 8 m / s
G 9.8 N / kg
Sound speed 340m / s in air at 15 ° C
The safety voltage is not higher than 36 v
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Basic concepts of junior high school physics
1、 Measurement
1. Length L: main unit: meter; measuring tool: scale; when measuring, it should be estimated to the next digit of the minimum scale; light year is the unit of length
2. Time t: main unit: second; measuring tool: clock; stopwatch in laboratory. 1 hour = 3600 seconds, 1 second = 1000 milliseconds
3. Mass m: the amount of material contained in the object is called mass. Main unit: kilogram; measuring tool: scale; pallet balance for laboratory
2、 Mechanical movement
1. Mechanical movement: movement in which the position of an object changes
Reference: to judge the motion of an object, another object must be selected as the standard
2. Uniform linear motion:
① Two ways to compare the speed of movement: a compare the distance traveled in the same time
B compare the time required to travel an equal distance
② Formula: v = s / T
③ Unit conversion: 1 m / S = 3.6 km / h
3、 Strength
1. Force F: force is the action of objects on objects. The action of forces between objects is always mutual
Unit of force: Newton (n). Instrument for measuring force: dynamometer. Spring scale is used in laboratory
The effect of force: to deform or change the state of motion of an object
The change of object motion state refers to the change of object velocity or motion direction
The three elements of force: the size, direction and action point of force are called the three elements of force
The diagram of force should be scaled; the diagram of force should not be scaled
Gravity g: the force exerted on an object due to the attraction of the earth
Relationship between gravity and mass: g = mg m = g / g
G = 9.8n/kg. Reading method: 9.8n/kg, which means the gravity of an object with a mass of 1kg is 9.8n/kg
Center of gravity: the point of action of gravity is called the center of gravity of an object. The center of gravity of a regular object is at the geometric center of the object
4. Balance condition of two forces: acting on the same object; equal magnitude of two forces; opposite direction
Under the balance of the two forces, a body can be stationary or move in a straight line at a constant speed
The equilibrium state of a body means that the body is in a state of static or uniform linear motion. The resultant force of the external force on the body in equilibrium state is zero
5. The combination of two forces on the same line: the direction is the same: the resultant force F = F1 + F2; the resultant force direction is the same as that of F1 and F2;
The direction is opposite: F = f 1 - F 2; the direction of the resultant force is the same as that of the larger force
Under the same conditions, the rolling friction is much smaller than the sliding friction
Sliding friction is related to normal pressure, material properties and roughness of contact surface
7. Newton's first law is also known as the law of inertia. Its content is: when all objects are not affected by external forces, they always keep static or uniform linear motion
Inertia: an object has the property of keeping the original static or uniform linear motion state, which is called inertia
4、 Density
1. Density ρ: the mass per unit volume of a substance. Density is a property of a substance
Formula: M = ρ V, international unit: kg / M & sup3;, common unit: g / cm & sup3;,
Unit conversion: 1g / cm & sup3; = 1 × 10 & sup3; kg / M & sup3;; ρ water = 1 × 10 & sup3; kg / M & sup3;;
Reading: 10 & sup 3; kg / m3, which means the mass of 1 cubic meter of water is 10 & sup 3; kg
2. Density measurement: mass measurement with pallet balance and volume measurement of solid or liquid with measuring cylinder
Area unit conversion:
1cm & sup2; = 1 × 10 ^ - 4m & sup2;,
1 mm & sup2; = 1 × 10 ^ - 6 M & sup2
5、 Pressure
Pressure P: the pressure on the unit area of an object is called pressure
Pressure F: force acting vertically on the surface of an object, unit: n
The effect of pressure is expressed by pressure, which is related to pressure and area
Pressure unit: n / M & sup2;; special name: Pascal (PA)
Formula: F = PS [S: the area under force, the common part of two objects in contact; unit: M & sup2;.]
Methods to change the pressure: ① reduce the pressure or increase the stress area, can reduce the pressure; ② increase the pressure or reduce the stress area, can increase the pressure
2. Internal pressure of liquid: [measurement of internal pressure of liquid: use liquid manometer (U-tube manometer)]
Causes: due to the gravity of the liquid, pressure is produced on the bottom of the container; due to the fluidity of the liquid, pressure is produced on the wall of the container
Laws: 1. At the same depth, the pressure in each direction is equal
② The greater the depth, the greater the pressure
③ At the same depth of different liquids, the liquid with higher density also has higher pressure
The formula is: P = ρ G H: unit: m; ρ: kg / M & sup 3;; g = 9.8 N / kg
3. Atmospheric pressure: the atmospheric pressure is produced by the action of gravity. It is the madeburg hemispheric experiment that proves the existence of atmospheric pressure, and it is Torricelli (Italian scientist) who determines the value of atmospheric pressure
The height of mercury column remains unchanged and the length of mercury column becomes longer after the torrix tube is tilted
1 standard atmospheric pressure = 76cm mercury column height = 1.01 × 10 ^ 5pa = 10.336m water column height
Instruments for measuring atmospheric pressure: Barometer (mercury barometer, box barometer)
Atmospheric pressure changes with altitude: the higher the altitude, the lower the atmospheric pressure, that is, the higher the altitude, the lower the boiling point
6、 Buoyancy
1. Buoyancy and its cause: an object immersed in liquid (or gas) is supported upward by liquid (or gas), which is called buoyancy. Direction: vertical upward; cause: pressure difference between liquid and object
2. Archimedes principle: objects immersed in liquid are subject to upward buoyancy, and the buoyancy is equal to the gravity of objects expelling liquid
That is, f floating = g liquid discharge = ρ liquid GV discharge
3. Buoyancy calculation formula: F floating = G-T = ρ liquid GV discharge = f upper and lower pressure difference
4. When the object floats: F floats = g and ρ g and ρ 2F
Mixed calculation of rational number addition, subtraction, multiplication and division
9 + (- 3) - (+ 3) times ⑤ / ⑦ =
Any place is OK
Finding monotone increasing interval and monotone decreasing interval of function y = sin2x
The increasing interval of SiNx is (2k π - π / 2,2k π + π / 2)
The minus interval is (2k π + π / 2,2k π + 3 π / 2)
So increasing here is 2K π - π / 2
Analysis, f (x) = root x, this function is increasing from 0 to positive infinity
Let g (x) = SiNx, which is a sine function
Let's discuss the original formula and find the definition field first, because the number under the root sign can't be negative
That is, 3x π is greater than or equal to π / 62k π and less than or equal to 5 π / 62k π
The domain of definition can be obtained by simplification, and the value of X must be in the domain
Then we begin to discuss the decreasing interval
Let f (x) = f [g (x)], if f (x)... Is expanded
Analysis, f (x) = root x, this function is increasing from 0 to positive infinity
Let g (x) = SiNx, which is a sine function
Let's discuss the original formula and find the definition field first, because the number under the root sign can't be negative
That is, 3x π is greater than or equal to π / 62k π and less than or equal to 5 π / 62k π
The domain of definition can be obtained by simplification, and the value of X must be in the domain
Then we begin to discuss the decreasing interval
Let f (x) = f [g (x)] be a new function. If f (x) is an increasing function, then if f (x) is a decreasing function, then G (x) is a decreasing function
So we can find the decreasing function interval of 2Sin (3x π) - 1
Then the intersection of the calculated value and the domain is OK
I'm sorry I don't have a way of thinking
Help junior high school physics all the formulas and all the symbols of the representative meaning
R resistance u voltage I current p power t time w work f force s area L length n surface north pole s surface South Pole in magnet
Well, I'd like a little bit of score addition, subtraction, multiplication and division
Addition, subtraction, multiplication and division are OK, multiplication and division are a little more
Just a few more points. The difficulty should be moderate!
5+14 9*32 64/2 33+51 36/9 82-41 9+2 56*4 33*5 66/11 77*6 88*2
9+12 8+63 78-26 47+32 36*10 95-28 31*9 32*8 39*4 40+58 60+43
35*1 1*34 3*63 4*7 9*73　　89*2 74*5 1*26 8*43 8*77　　3*6= 8*79 6*19 1*2 6*7 87*8 87-31 5*38 4*23　　78*8 82-51 74*2 37*6 76*1 79*6
9*66 41*9 8*34 3*86 6*17　26+31 99-25 　1*77 24*9 1*25 72*6 3*18
72*2 6*95 35+14 3*59 9*91 6*98　　2*96 66-16 78*6 7*95 83*4 8*31
2*8= 31*9= 7*73= 6*42= 1*58= 99*2= 94*8= 5*12= 5*45= 6*71=
5*47= 13*7= 64*2= 75*9= 2*32=　 80-73= 92-48=　 3*20= 6*88= 11*8= 21*2= 59*1=　30-22= 　43*3= 52*3= 43*6= 36+15= 29*6= 30*7= 8*25= 96*6= 31*2= 4*49= 70-49= 7*29=　99-37=　6*80= 30-20= 7*37= 1*6= 65*9= 70*6= 62*6= 80-30= 81/9= 71-39= 66-17= 80-56= 90-67= 90-91= 70-45= 90-10= 40-3= 80-61= 30-13= 60-66= 70-43= 70-2= 80-53= 60-53= 50-16= 70-55= 70-58= 70-52= 40-47= 40-10= 90-32= 90-76= 60-56= 80-30= 30-10= 70-48= 24+31= 20+68= 41+53= 22+62= 52+26= 38+13= 44+40= 40+35= 16+79= 63+14= 59+23= 39+35= 63+35= 47+19= 41+32= 18+75= 41+53= 85+6= 37+38= 16+45= 74+21= 25+56= 41+25= 44+14= 27+50= 48+31= 44+38= 19+19= 12+88= 4+64= 68+22= 29+40= 58+2= 91+3= 17+50=
46+48= 23+60= 73+10= 22+37= 39+34= 38+33= 48+34= 30+58= 34+36= 61+5=
44+40= 40+49= 89+9= 51+37= 20+77= 36+35= 50+42= 36+38= 47+45= 76+23
The monotone increasing interval of function y = sin2x is
Because the function y = sin2x;
Let 2K π - 2 π ≤ 2x ≤ 2K π + 2 π & # 8658; K π - π ≤ x ≤ K π + π
The monotone increasing interval of function y = sin2x: [K π - π, K π + π], K ∈ Z
Unit (meaning of unit) and definition
It's mechanics, isn't it anything else