2 junior high school physics questions, help me solve 2 junior high school physics problems?

If the direction is opposite, the direction of the resultant force is the same as the general direction. But the magnitude of the resultant force is the difference between the two forces. (2) Then look at the lever around that point after adding force.

3) Of course, junior high school is not difficult, knowledge is gradual, it is impossible to tell everything at once, do you have to learn it in the future? The leverage should not be very difficult, but the buoyancy is somewhat difficult.

First of all, junior high school physics is actually not very difficult, and the more difficult to understand may be the first chapter of the first volume of the 8th grade, where there are some formulas and calculations for buoyancy pressure. The rest is basically memorization. You're right, there will be an in-depth physics to high school, but if you study science, buoyancy is not much talked about, (there are electives), and leverage is basically not talked about.

I mainly talk about Newtonian mechanics and kinematics, and then I will also study electromagnetism, which is perhaps the most difficult, and there are many formulas, but I think as long as you understand it, the formulas can be deduced.

Question 1: (1) Because R1R2 is connected in parallel, U1=U2=U=24V, according to I=U R, R2=U I2=24V Ω.

You can find R1 current, add R2 current = total current, total voltage Total current = total resistance, re-derivation formula R2, the process is not written.

2 kick: No, i=u r is Ohm's law, and the definition of the derivation formula r=u i should also be based on Ohm's law: when the voltage is constant, the current is inversely proportional to the resistance; When the resistance is constant, the current is proportional to the voltage.

If you have to say that, it is also when the current is constant, and the resistance is proportional to the voltage; When the voltage is constant, the resistance is inversely proportional to the current.

1).r2=u2 i2=24v beaten. 2).

i1 = u1 r1 = 24v 80 ohms = and = i1 + i2 = . r and = u i and = 24 euros. r2=r1r-(r1-r)=80x48 (80-48)=120 ohms.

2.Wrong. Without combining the laws of physics, deformation in a purely mathematical sense has no physical significance.

Resistance is an inherent property of a conductor, which does not change due to external voltage and current, and cannot be said to be proportional and inverse. Resistance is a constant and does not change with variables. Experiments show that the voltage is n times of the original, the current is also n times of the original, and the ratio is still r.

The circumference of the circle has become n times the original, and the radius is n times the original, has it changed?

1.The amplitude of the first toggle of the saw blade is large, and the second time is small, i.e., the greater the amplitude of the mechanical wave, the greater the intensity of the wave.

2.(1) Vacuum, e.g. on the moon (2) Sound source control, e.g. barrel muffler (3) Acceptance control, e.g. earbuds.

1. Appearance: Echolocation.

2 uh. I don't know. I also have two drops at the beginning of the prime.

1.It shows that the loudness of the sound is related to the amplitude, and the greater the amplitude, the louder the louder!

2.It can be loud enough to cause human hearing!

It can also be a problem with the hearing ability of the human ear, such as deafness.

It can also be the lack of propagation medium, and the vacuum cannot transmit sound!

1) Obtained by =m v: A: B = 1/2: 2/5 = 5:4

2) Obtained by =m v: m is inversely proportional to v when m is certain, and saline water alcohol , so v saline v water v alcohol.

So the highest alcohol.

Dumbo's good sound is transmitted by the air, and closing the doors and windows isolates most of the c

1.Xiaofei's method is good, because in this way, everyone can take what they need, and it is comfortable.

Wrong, because who is the electronic organ imitating? C: That's right.

1.In order not to affect the hobbies of others and not to torture himself, Xiaofei's method is preferable, although it cannot be isolated, it can effectively reduce the intensity of the sound.

It all makes sense that the first is attenuated at the beginning of the sound source, the second is attenuated during propagation, and the third is attenuated at the reception cEcho is a phenomenon of sound reflection.

1.Used together. Xiaoying's method is to prevent dry sounds, Xiaofei's method is to block the spread of dry sounds, and Xiaohai's method is to prevent dry sounds from entering his ears. So it's better to use them together.

1, Xiaofei is right, because air cannot travel in a vacuum2,c

1.Xiaoying's method is good, directly from the distance to reduce the noise.

The correct option is: a

Because a small black dot is stained on the convex lens, because the small black dot is located within the collection distance of the convex lens, it will not form a real image on the light screen. So there won't be a small black dot on the light screen. If there is no small black dot, the image of the candle flame will be slightly darker, because the small black dot will block some of the light coming to the light screen.

Hope it helps.

The answer is a

However, the brightness of the image is lower than that of the convex lens without black spots, that is, the image is slightly darker.

The reason for this is that the light that should be reflected behind the lens is blocked.

Choose a for this question. The reason is that in the image of the candle flame, it is crossed through the convex lens, not horizontally through the convex lens.

a Because it does not affect the refractive imaging of light in other positions, even if part of the lens is obscured.

The first problem is similar to the physics competition problem in a city this year, the effect is to melt them in frost or snow weather, making them easy to drive, the principle is very simple, Joule's law.

The second question, this is actually not related to the left and right hands at all, but people have found such a feature after many experiments, and summarized her according to this law, there is no point in you entanglement with this problem, in fact, the teacher told us that you can also use the "right hand responsibility" to determine the motor, but the method is different.

1. When the electrons are running in the conductor, they collide with each other, generating heat, and the thermal effect of the electric current, the temperature is high enough to a certain extent, it will work, and it can be used for defrosting, etc., 2, this is the conclusion (that is, coincidence) that the older generation of scientists came to by chance after tens of thousands of experiments and has no complete connection with the hand.

1A: The function of the metal film is to volatilize the water droplets on the rear glass into water vapor through the heating of the metal film, so as to maintain a good view of the rear window. The principle is to use the metal wire in the metal film to generate heat. The metal wire is a resistance wire. q=i2rt