Please help me solve the physics problem of the third day of the first grade It's like this: Xiao Ming wants to use 20 C cold water and 100 C boiled water to get 40 C warm water. What's the mass ratio of cold boiled water?

If there is no heat loss, there are:
Q suction = q discharge
That is, CM cold (40-20) = CM HOT (100-40)
So m cold: m heat = 60:20 = 3:1

G = 10N / kg
1. If a cube with a length of 10 cm on one side is immersed in water and its upper surface is 15 cm away from the water surface, the pressure difference between the front, back and both sides of the object is the same___ What is the pressure difference between the upper and lower surfaces of an object under water_ What is the buoyancy of an object Cattle
2. There is a metal ball hanging from the lower end of the spring scale. The indication of the spring scale is 10N. When the metal ball is immersed in water, the indication of the spring scale will change The buoyancy of the metal ball will decrease If half of it is immersed in water, the indication of the spring scale is 9N, and the buoyancy of the metal ball is 9N__ Cow; if you immerse it all in water, the indication of the spring scale will change to_ Cattle
3. Ships: made of materials that are denser than water____ And make it work_ More water, more buoyancy It's made of the truth_____ It's called displacement
4. Balance method_ (suitable for floating and suspending)

(1) 0 N: the front, back and both sides are at the same depth of water, P = pGH, and the pressure at the same depth is equal, so the difference is zero
2 N: F = PGs (h2-h1) = 1000 * 10 * 0.01 * (0.15-0.1) = 2
2 N: buoyancy is the pressure difference between the upper and lower surfaces
(2) . decrease: when the metal ball is subjected to upward buoyancy, the tension on the spring decreases
Increase: buoyancy is proportional to the volume of the liquid being drained
1 N: F float = G-F pull = 10-9 = 1
8 N: the buoyancy is proportional to the volume of the liquid, half of the buoyancy is 1 N, all immersed is 2 n
(3) . hollow: can increase volume
Line up:
Archimedes principle;
Quality of boiled water: according to Archimedes' principle, f floating = g row, ship is floating, G ship = f floating, that is, G ship = g row, m ship g = m row, m ship = m row
(4) . g = f

As shown in the figure, a uniform plank is 15m long and 400N in weight. It is symmetrically placed on two supports a and B 8m apart. A person with a weight of 500N starts from point a and walks left to point a______ M, the board will start to tilt

The weight of the board is g = 400N, the length of the board is 15m, and the center of gravity is on the middle point of the board. Take a as the fulcrum, then the center of gravity of the board is 4m to the right of point a, that is, the force arm of the board gravity L1 = 4m. When people (weight is g '= 500N) walk to the left far away from point L2, the board will start to tilt. According to the lever balance condition: GL1 = g' = l2400n × 4m = 500N × L2L2 = 400N × 4m500n = 3.2m, the answer is: 3.2

A thin-walled cylindrical container with a gravity of 2n, a bottom area of 1.0 × 10 ^ (- 2) m ^ 2 and a height of 0.13M contains water with a gravity of 12n. Now it is placed on the horizontal ground
(1) The pressure of water on the bottom of the container
(2) Depth of water in container
(3) When a 540g aluminum block is immersed in water, the pressure of the container on the horizontal ground. The known density of aluminum is 2.7 × 10 ^ 3 kg / m ^ 3
Mainly the third question,

It seems that the third question is very simple, but pay attention to calculate the volume of the cylindrical container. When using P = f / s, the volume of the cylindrical container is v = 1.0 × 10-2 M2 × 0.13M = 1.3 × 10-3m3; the volume of water is V1 = 12 △ 10 △ 1.0 × 103m3 = 1.2 × 10-3m3; the volume of aluminum block is V2 = 0.54 △ 2.7 × 103 =

A 2m long wooden stick, thick at one end and thin at the other, is placed on the horizontal ground. If the thick end of the stick is slightly lifted off the ground, it needs a force of 80N. If the thin end of the stick is slightly lifted off the ground, it needs a force of 70N. What is the weight of the stick? Center of gravity to thin end? rice

If its thick end is slightly lifted off the ground, it needs a force of 80N. If its thin end is slightly lifted off the ground, it needs a force of 70N

Is physics difficult in grade three? Where should we preview first?

If it's just for the exam, it's not very difficult,
Preview before class and do corresponding exercises (right or wrong)
Pay attention to the content of the teacher's analysis and the process of the experiment
Any questions you don't understand or understand should be considered and consulted
Consolidation training after class
But it's not easy to really learn physics well

"Low carbon life" is a green lifestyle advocated by today's society. How much less bituminous coal can be burned by heating 2000 kg of water from 15 ℃ to 50 ℃ with solar energy? [suppose that the calorific value of bituminous coal is 2.94 × 107j / KGC, water = 4.2 × 103J / (kg ·℃)]

The heat absorbed by water from 15 ℃ to 50 ℃ q = C water m water (t-t0) = 4.2 × 103 × 2000kg × (50 ℃ - 15 ℃) = 2.94 × 108j; the mass of fully burned coal is m = QQ = 2.94 × 108j 2.94 × 107j = 10kg; a: it can burn 10kg less bituminous coal

Preview of colorful material world
When measuring density, we often use balance and measuring cylinder. So, what are the rules of using balance and measuring cylinder?

1、 Rules for use of balance:
It can be summed up into 24 words: "on the horizontal platform, you code return to zero, beam balance, left object right code, first big then small, beam balance."
(1) "Look": observe the weighing of the balance and the graduation value of the traveling code on the scale
(2) "Put": put the balance on the platform to ensure the balance level; put the traveling code on the zero mark on the left end of the scale
(3) "Adjustment": adjust the balance nut at the left or right end of the balance beam to make the pointer at the center line of the dividing plate or the swing amplitude of the pointer equal, then the beam is balanced
(4) Weighing: put the measured object in the left disk, add and subtract weights in the right disk with tweezers, and adjust the position of weights on the ruler until the beam is balanced
(5) Note: the mass of the measured object = the total mass of the weight in the plate + the scale value of the moving weight on the ruler
2、 Usage rules of measuring cylinder (or measuring cup)
Can be summed up as "three words" policy: look, put, read
(1) "See": before use, you should see the range and division value (the volume indicated by each small grid); the volume unit of measuring cylinder (or measuring cup) is generally ml (ML), that is cm ^ 3
(2) "Put": when measuring, put the measuring cylinder (or measuring cup) on the horizontal table
(3) "Reading": when reading, the line of sight should be level with the convex top (such as mercury, etc.) or concave bottom (such as water, etc.) of the liquid in the cylinder. Otherwise, the reading will be inaccurate (Note: the reading is too large when looking down, and too small when looking up)

In the age of dinosaurs, the oxygen content in the atmosphere accounted for 10%. 50 million years ago, the oxygen content in the atmosphere rose to 17%. 40 million years ago, the oxygen content in the atmosphere reached 23%. At present, the oxygen content in the atmosphere is 21%
How to make the oxygen content in 200 liter air 10% of that in dinosaur era

200 times 21 percent = 42 liters, 200 times 10 percent = 20 liters, 42-20 = 22 liters, extract 22 liters of oxygen

Mathematics problem evaluation manual
From Nanjing to Shanghai, car a runs for 4 hours and car B runs for 5 hours. How much faster is car a than car B?
fast

Let the whole distance be x meters, the speed of a be x / 4, and the speed of B be x / 5
(x / 4-x / 5) / (x / 5) = 1 / 4 = 25%

Please help me solve the physics problem of the third day of the first grade It's like this: Xiao Ming wants to use 20 C cold water and 100 C boiled water to get 40 C warm water. What's the mass ratio of cold boiled water?