In the second year of junior high school, choose one of the three physics problems

1.The first one won't be that how many decibels are hard elephant sonar (as if it were) the movement of the earth's crust

2.Because you speak and listen to yourself, there are two mediums: one is air, and the other is your body.

In the experiment, you can listen to one sound in two mediums, such as a tuning fork, one with air, and one with a desktop.

Conclusion The same sound is transmitted differently through different media.

3.No.

It's a math problem: one ear can't determine a point, it can only determine a line.

Conclusion: I Khan What kind of conclusion do you want?

Of course, there's another answer to this question, which is to use one ear to listen to the same sound source in a different position, and you can determine the location of the sound source.

**Infrasound ,... can be emittedWhen people speak, they are sounded by bodily substances such as bones, and when they are recording, they are sounded by air, and the sound sounds different ,... different mediumsIt is not possible to tell which side is because people rely on the stereo sound of binaural fossa receptors.

3. No, one ear can only distinguish the approximate direction, but it can't determine the exact location There is an intersection point for the sound heard by the two ears, which is equivalent to two straight lines crossing each other, to determine the same point.

1. Infrasound is a sound wave with a frequency of less than 20Hz (Hertz). Elephants, hippos, giraffes, whales. can be made and heard. Volcanoes** and the like can emit infrasound.

2. The sound you hear has been transmitted to your ears directly through muscle vibration, and listening to your own echo is different from recording, first of all, it is transmitted through air vibration, which is the difference, and in addition, it is difficult to guarantee that the recording will be distorted (limited by the equipment).

3. People judge the direction of sound according to the strength of the sound received by the two ears.

People with normal hearing in both ears can use either ear to distinguish the direction of sound.

As for the experiment, you can try it yourself.

2.Why does listening to your own recordings feel different from your own voice?

Because recording is the sound that travels through the air, while the sound you hear is in a solid, the sound travels differently in different states.

s=60m

v=10m/s

t=s v=6s (here is the time from the bus to the midpoint of the zebra crossing.) ）t=6s

s = 8m + the bus has a width).

v=s t=Here is the speed required by Xiao Wang to cross ab. )

s=60m

v=10m/s

t=s v=6s (here is the time from the bus to the midpoint of the zebra crossing.) "Along the AB" across the road, what direction is this AB? Let's go in the direction perpendicular to the road.

Since the bus was driving in the middle of the road, this student could walk out of the AB direction within 6 seconds.

s = m t = 6 seconds.

v=s t is about meters and seconds.

3) The density of cube b is 2kg dm 3 is greater than the density of water 1kg dm 3, so b sinks to the bottom of the water;

The volume of cube b is 1dm 3, the mass of the same volume of water = 1dm 3 1kg dm 3 = 1kg, 1kg 10n kg = 10n, and the buoyancy of cube b is 10n (ox).

2.You can't choose A, the correct answer is D

Because the voltmeter should be connected in parallel with the bulb under test, not in series with the bulb, there is an error that the voltmeter is connected in series with the bulb in all three options.

1. Smooth inclined plane, so the friction is negligible, and the options c and d with friction are excluded.

2. The object on a smooth inclined plane is not affected by friction According to Newton's first law, the object maintains a uniform linear motion and is no longer affected by thrust Exclude b

So choose A

During the movement, there is no friction on the smooth inclined plane, and the thrust only has the effect of spring elongation, not when sliding.

The supporting force is perpendicular to the bevel. Supporting role.

Because it has already been said that the bevel is smooth, there is no friction, only gravity and support.

The title says that there is a smooth bevel and no friction.

The 15° problem is the angle of change. That's 15°, which means that the landlord thinks too much.

The angle at which the propagation direction of the light changes: If the light travels in a straight line, then it should be in the direction of the red dotted line, and now due to refraction, it becomes the direction of the refracted light you drawn, deflected (15°).

Don't be impatient, take your time.

1. Becoming longer (the mercury column becomes a parallelogram, which is considered as the diagonal length, so it becomes longer; The cross-section of the mercury column becomes larger, and the pressure becomes smaller, so the gas column becomes longer).

2. Take the plate as the research object, let the right rope tension be x, then the middle one is also x, the leftmost one is 2x, and solve the equilibrium equation to get x =, then it is a bit difficult to say that it is a bit difficult for the second year of junior high school, and the standard of 20 years ago is a competition problem.

The length of the first one remains the same, because the density of the two is different, so it is impossible to dissolve, and the second one can't see clearly, is the person standing on the plank?