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Anonymous users2024-02-06The topic of the second year of junior high school is nothing more than the focus of the three states of solid, liquid and gas, and it is recommended to buy this textbook to fully interpret it, and everything is OK.
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Anonymous users2024-02-05Questions about what to ask.
Optics, acoustics, electricity, or something else?
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Anonymous users2024-02-04Chen Ming wants to compare the sound insulation properties of several materials (clothes, tin foil, styrofoam), please participate in the experiment**:
1) Experimental equipment: In addition to the materials to be tested and shoeboxes, there are also tuning forks and mechanical alarm clocks. Among them, the one that is suitable as a sound source is because of .
2) Experimental design: Chen Ming put the sound source into a shoebox and stuffed it with the filler material to be tested. The following two experimental schemes, A and B, are designed, and you think the best one is ( ).
a Stand at a distance from the shoebox and compare the loudness of the sounds you hear.
b Listen to the sound and step back until you can't hear it, comparing the distance from the shoebox.
At the school sports meeting, the 100m race is in full swing, ask:
2) If the timekeeper only clocks the time after hearing the "run" sound, how much will the athlete's performance be improved? (The speed of propagation of sound in the air is known to be 340 m s).
The incident ray is at an angle of 60° to the plane mirror, then the angle of reflection is:
a．30° b．60° c．90° d．40°
Xiao Ming thought when he saw the mirror hanging on the wall in the classroom:
1. When light is reflected on the mirror surface, the angle of reflection is the angle of incidence.
2. The "reflective" phenomenon occurs on the blackboard in the classroom, which is caused by the fact that the blackboard is too smooth.
3. The object can be imaged in a plane mirror. Xiao Ming said: "The distance from the image of the object in the plane mirror to the plane mirror is equal to the distance from the object to the plane mirror." Can you prove the above statement true experimentally? Please describe your experiment briefly.
When Xiao Ming moves an apple from 1x the focal length away from the convex lens along the main optical axis to 4x the focal length from the convex lens, the size of the apple image:
A does not change, B gradually decreases, C becomes larger first and then smaller, D becomes smaller first and then larger.
A concave lens and a convex lens can be used to make a mirror, and two convex lenses with different focal lengths can be used to make a mirror, and a mirror can also be made. If it is used to observe small objects, it is necessary to use the focal length as the objective lens and the focal length as the eyepiece.
Xiao Ming wants to dry the wet clothes as soon as possible, and the following practices are wrong:
A Hang wet clothes in the shade B Hang wet clothes in a sunny place.
c Put it in the washing machine to dry d Spread out the wet clothes and dry them in a ventilated place.
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Anonymous users2024-02-03Analysis: = mv, i.e. density = mass volume. The following conclusions can be derived from this formula:
1.When the density of the two substances to be compared is the same, the mass and volume are proportional (or the ratio of the masses of the two substances is equal to the ratio of volume); 2.When the two substances to be compared have the same mass, the density and volume are inversely proportional; (Or that the ratio of density is equal to the reciprocal of the ratio of volume, for example, the ratio of density is 2:.)
3, the volume ratio is 3:2); 3 .When the volume of the two substances to be compared is the same, the density is proportional to the mass (that is, the ratio of density to mass is the same; For example:
When the ratio of density is 3:4, the ratio of mass is also 3:4).
Based on this conclusion, many problems related to density ratios can be solved very quickly.
Answer:1Because the volume of the bottle is a constant quantity, or the volume of the two substances is the same, in accordance with the third article in the analysis, since the density of water is water = and the density of alcohol is wine = , the ratio is 1:
Then since the water can hold 2kg, then of course the alcohol is.
2.The title has made it clear that both substances are solid and have the same volume, so consistent with the third article in the above analysis, the ratio of matter is 2:3, that is, the ratio of mass is 2:3, and the ratio of density is also 2:3.
3.The third question, I don't know if you wrote it wrong, if it wasn't if you wrote it wrong, then this steel ball must be hollow.
But I can help you explain the solution:
Idea 1: Calculate how much mass a 7m steel ball should have, compare it with the mass given in the question, if it is equal, it means that the steel ball is solid; If the calculation result is greater than the mass given by the question, it means that it is hollow, and if it is less than the mass given by the question, the problem is wrong.
Idea 2: Calculate how much the volume of the steel ball should be, compare it with the volume given in the question, if it is equal, it means that the steel ball is solid; If the calculation result is less than the volume given by the question, it means that the steel ball is solid, and if it is greater than the volume given by the question, the question is wrong.
Using the results in idea 2, the volume of the hollow part ( Fe =
4.Measuring density with a balance can be seen as the same mass of two substances, so the second clause in the analysis is used, and the density is inversely proportional to the volume. Simply measure the volume of the effluent and another liquid. Formula Water: liquid = v liquid: v water.
5.Both times it is full, so that means the volume is the same. All remove the mass of the bottle then can be filled with 500g of water, can be filled with another liquid of 400g, water:
Liquid = m water: m liquid, substitution, : liquid = 500g:
400g, then you can calculate the knot.
The above is a little bit of my personal experience, I hope it will be helpful to you.
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Anonymous users2024-02-02Go buy this top student and all the problems are solved.
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Anonymous users2024-02-0120 degrees Celsius is the speed of sound 340m s
1.Taking the place where the sound is made, and the distance from the starting point to the cliff is s, then the total distance between the car and the sound in these 4 seconds is 2s, so 2s = 4 * 8 + 340 * 4, and the solution is s = 689m.
2.In general! The speed of sound propagation in solids is greater than that of liquids than in gases!
The first time is the medium of sound, iron, and the second time is sound, because 918 340=, it takes seconds to transmit sound in the air, and it takes seconds to transmit sound in iron pipes, so v=918
Sorry, I don't know how many I can hear.
s=255m
If both balls of equal volume A and B float on the water, then the buoyancy received by the two balls of A and B is equal to the gravitational force received by A and B respectively, but A and B are only equal in volume and do not know the density, so the amount of buoyancy they receive cannot be determined, so D is chosen. >>>More
The salesperson said that the microwave oven is very energy-efficient, that is, it has a high energy efficiency ratio. >>>More
In the second question, it is necessary to understand the principle of buoyancy. The buoyancy force is only related to the volume of the dispelled liquid and the density of the liquid, i.e., f float = liquid density p the volume v of the dislodged liquid of the object v gravitational acceleration g. The nut falls out, but it should be noted that the whole bottle is suspended in the question stem, indicating that the whole bottle is immersed in water, and the volume v row of the estimated water body is still equal to the volume of 3 bottles, and there is no change. >>>More
Answer D Analysis: Taking the passenger as the reference, the relative direction of movement of the motorcycle is the northwest direction, and the relative movement speed is decomposed into the velocity v0 in the west direction and v1 in the north direction. >>>More
25-2)/(25+1)=(60-2)(t+1)t=
95-5) (100-0) = (32-5) (t-0) t = 30 degrees Celsius. >>>More