1. After the reform and opening up, many rural areas are irrigated with automatic sprinkler irrigation equipment. The water pipe is higher than the ground, and there is an automatic rotating sprinkler head at the top of the water pipe. The distance h (m) between the water flow from the sprinkler and the ground point and the water pipe satisfies the relationship H = (negative) - 1 / 2S square + 2S + 1.5, Does the distance h from the ground increase or decrease? 2. Try to write a binomial expression of three times to make it meet the following requirements at the same time: (1) It can be extracted from the common factor; (2) it can be decomposed by the square difference formula ————————- (fill in the blanks)—————————— Using factorization calculation: 3.2005 square * 0.25-4008 * 2005 * 0.25 + 2004 square * 0.25

1. After the reform and opening up, many rural areas are irrigated with automatic sprinkler irrigation equipment. The water pipe is higher than the ground, and there is an automatic rotating sprinkler head at the top of the water pipe. The distance h (m) between the water flow from the sprinkler and the ground point and the water pipe satisfies the relationship H = (negative) - 1 / 2S square + 2S + 1.5, Does the distance h from the ground increase or decrease? 2. Try to write a binomial expression of three times to make it meet the following requirements at the same time: (1) It can be extracted from the common factor; (2) it can be decomposed by the square difference formula ————————- (fill in the blanks)—————————— Using factorization calculation: 3.2005 square * 0.25-4008 * 2005 * 0.25 + 2004 square * 0.25

H = - 1 / 2S (2) + 2S + 1.5 h (1) = - 1 / 2 * 1.9 (2) + 2 * 1.9 + 1.5 h (1) = - 0.5 * 1.9 * 1.9 + 2 * 1.9 + 1.5 h (1) = 3.45 H (2) = - 1 / 2 * 3.9 * 3.9 + 2 * 3.9 + 1.5 h (2) = 1.695, the flow drops by the square of 2005 * 0.25-4008 * 2005 * 0.25 + 2004 * 0.25 = 0.25

As shown in the figure, the specification of the small bulb is "6V & nbsp; 3.6W" (filament resistance does not change), close the switch, when the slide P of the sliding rheostat moves to the a end, the current indication is 0.6A; when the slide P moves to the B end, the voltage indication is 4V, then ()
A. The filament resistance of the small bulb is 6 Ω B. the power supply voltage is 10vc. The maximum resistance of the sliding rheostat is 10 Ω D. when the slide P is located at the B end, the power consumed by the sliding rheostat is 0.8W

A. RL = U2, P = (6V) 23.6w = 10 Ω, so a is wrong; B. when slide P moves to end a, there is only lamp L in the circuit, I = 0.6A, power supply voltage U = IR = 0.6A × 10 Ω = 6V, so B is wrong; C. when slide p moves to end B, all slide rheostat is connected as resistance R, lamp L and R are in series, ur = 4V, UL = u-ur = 6v-4v = 2V, ∵ I = URR & nbsp; = & nbsp; The results show that: ulrl, r = urrlul = 4V × 10 Ω, 2V = 20 Ω, so C is wrong; D, ur = 4V, r = 5 Ω, PR = u2rr = (4V) 220 Ω = 0.8W, so D is correct

Two physics problems in the second grade of junior high school (about buoyancy)
1. Two skis are used by skiers, each of which is 2m long and 10cm wide. If the skier's mass is 50kg and the total mass of skis is 12kg, what is the pressure and pressure on the horizontal snow?
2. The volume of the underwater part accounts for three fifths of the total volume of a 200 cm ^ 3 wooden block floating on the water surface?
Briefly write the calculation process and ideas

1. Two skis are used by skiers, each of which is 2m long and 10cm wide. If the skier's mass is 50kg and the total mass is 12kg, what is the pressure on the horizontal snow? F pressure = 50kg * 10N / kg + 12kg * 10N / kg = 620np = f pressure / S = 620n / [(2m * 0.1M) * 2] = 1550pa2, volume is 20

Students all know that if two bulbs with the same rated voltage and different rated power are connected in parallel to the home circuit, the bulb with higher rated power will light up. If these two bulbs are connected in series to the home circuit, who will light up? Please make a guess and explain the reason

When two bulbs are connected in series, according to the power calculation formula P = I2R, because the current in the series circuit is equal everywhere, the greater the resistance, the greater the actual power, the brighter the bulb. Answer: guess: the bulb with lower rated power is brighter; reason: in the series circuit

1. Is the reflection of photographic film to all kinds of color light the same as that of human eye? Brief reasons
2. When there is a thunderstorm in summer, a student hears the thunder after seeing the lightning for 3S. Why did he see the lightning first and then hear the thunder? How far is the place where the thunder is produced from the student?
Remark: the temperature was 15 degrees at that time
Yes, five more points
What is the unit of 1020?

It's not the same, because the human eye can't see infrared and ultraviolet rays, but the photographic film is sensitive to both
The difference in time to the ground is so great because light travels 300000 kilometers per second, while sound travels only 0.34 kilometers per second in the air. The speed of sound is only one hundredth of that of light
How many seconds is the interval from seeing lightning to hearing thunder? Multiply by 340 meters, that is the distance from lightning to you. 3 * 340 = 1020

1. Record your voice on the tape, then listen to it. You will find that the recorded voice is different from the one you usually hear. Try to explain the reason for this phenomenon (using the knowledge of sound)
2. The speed of a jet plane is 1.5 times that of sound in the air, flying at an altitude of 3060m, flying horizontally. When you hear the roar of the plane above your head, look up (excluding the time of looking up), how far (horizontal distance) has the plane gone in front of you? (the speed of sound in the air is 340m / s)
The second is clear

What you hear from the tape recorder is transmitted through the air, and what you hear is transmitted through the jawbone. Different media lead to different communication effects
2 3060/1.5=9s
340×1.5=510m/s
510×9=4590m
It is 4590m
Probably. I'm a freshman now. I'm a little fuzzy. I remember the first question is not so accurate

1. There are three light balls a, B and C, of which only two are charged. When a and B are close to each other, they attract each other
If C repels each other when they are close to each other, then the uncharged ball is
A. B. B. C. C. D. can't judge
2. Put an object gently into a beaker filled with water and overflow the water with a weight of 0.3n, then the gravity it receives is:
A. Must be equal to 0.3n B. must be greater than 0.3n
C. Greater than or equal to 0.3n D. less than or equal to 0.3n

1.A;2.C

1. What's the reason for parachutists jumping off the plane and accelerating when the parachute is not opened? What's the reason for parachute's constant speed landing?
2. Xiaoming uses 20n force to push the car forward at a constant speed on the horizontal road. How much resistance does the car suffer from the ground? Why?

1. Before opening the parachute, it is subject to gravity and part of the air resistance, and the gravity is greater than the resistance, so it accelerates. After opening the parachute, the gravity does not change, the resistance becomes larger, and finally the gravity equals the resistance, so the speed is uniform
20 N, the force is 20, the reaction is also 20. Xiaoming moves at a constant speed, so the resistance is 20

16. The device as shown in Figure 1 can be composed of inclined plane, trolley, scale and sheet metal. The device and stopwatch can be used to practice measuring the average speed. The steps are as follows:
(1) keep the slope very small, put the car on the top of the slope and the metal sheet on the bottom of the slope, and measure the distance between the car and the metal sheet S1 = 0.5m
(2) let the car slide down from the top, and start to record the time at the same time. Measure the time T1 = 1 second when the car slides to the bottom and hits the metal sheet
(3) according to the measured S1 and T1, calculate the average speed V1 of the car through the whole slope
(4) move the sheet metal to the middle point of S1, measure the time T2 = 0.7 seconds for the car to slide from the top of the inclined plane over the upper half of the distance S2, and calculate the average speed V2 of the car through the upper half of the distance
(5) calculate the time T3 and average speed V3 for the car to pass the lower half of the distance
According to the above experimental steps, calculate V1, V2, V3, and explain what motion the car is doing when it slides down on the slope by comparison?

Where is the picture?

1. When an object with a mass of 0.5kg is hung on the lower end of the spring dynamometer, and the object is immersed in water, the indication of the dynamometer is exactly zero. When the object is immersed in another liquid, the indication of the spring dynamometer is one fifth of the gravity of the object. Find out (1) what is the volume of the object? (2) what is the density of the other liquid?

Objects can float in water, so the density is 1000
Volume 500 cc
The buoyancy of another liquid is four fifths of its own gravity
So the density of liquid is four fifths of the density of water, 800 cubic meters per kilogram