A reflection question about junior high school physics

It's different, I don't think it's my own voice, because I usually hear my own voice through the bones, but listen to the tape through the eardrum, and the effect is different.

Other students think it's your voice, because they usually hear through the eardrum as they listen to the tape.

What others think is the same, what you think is different.

Because for oneself, the sound that I usually hear is transmitted by solid (at least part of it is transmitted directly to the ears through the body), but the sound in the tape recorder is transmitted by the air. In the same way, to classmates, both are airborne and sound the same.

The sound you hear is mainly received through bone conduction (solid can transmit sound) The sound quality is maintained in all aspects, of course, it sounds better (your own voice thinks it is of course good), and the sound that others hear is transmitted through the air, and the sound quality is distorted in all aspects, which is definitely different from the voice you hear.

When recording, it is also transmitted through the air, so when recording, compared with others, the voice speaker feels that the sound he hears changes greatly, and the perception of others does not change much, especially for high-fidelity audio, others hardly feel the change.

The power is 40kw, and the work done in 25min is: (40x1000x25x60) joules.

Driving at a constant speed, the distance traveled is: s=vt, p=fv, p=40x1000x25%, f is the resistance, and the traction force of the constant speed driving is equal to the resistance.

The mass of gasoline: mq = 40x1000x25x60

Solution: 1) P=40kw=40000W, t=25min=1500SW=pt=40000wx1500S=6x107J2) from W =fs=fs to get S=W f =6x107j 2000N =3x104m

3) q=w has 25% =

m=q/q= =

If you have any doubts, you can ask them, hope.

2. After putting the stone into the water, the water surface is raised by 2 cm, and the volume of the water raised by 2 cm is 100 cubic centimeters, and the surface area of the water, that is, the bottom area of the container, is 50 square centimeters. The triangle H reads Delta H, which indicates the elevated G height, and since the original height (depth) of water is 10 cm, the volume of water in the container is 500 cubic centimeters, the mass is kilograms, and the weight is 5 Newtons.

May you learn and progress!

This is a method of draining the volume of an irregular object, and the volume of the water discharged by the object submerged in water is equal to the volume of the object

The first step is to find the bottom area of the cup because the stone is 100 cm3 and the water rises by 2 cm.

The second step is to find the total volume of water according to the bottom area of the cup and the height of the water in the original cup.

The third step is to find the gravitational force of water by multiplying the density by the volume and then by g.

s is the base area (which can be understood).

v is the volume. Volume can be used to find gravity.

The rise in the water level is due to the input of ice stones.

Ice cube volume = 100 6 = 600cm

The drop in water level is caused by the melting of ice into water.

A drop in water surface is a decrease in volume by 100

Since the density of the ice cube is twice that of water, the volume of pure ice in the ice cube is 56 (so that the volume of the stone in the ice cube = 600-560 = 40cm is obtained, and the ice cube is put into the bucket and the water is just suspended in the water, and the total mass of the ice cube is 600 1 = 600g

Whereas, the mass of pure ice in the ice cube is 560

So the stone mass is 600-504 = 96g

So the density of the stone is 96 40=

It is known from the suspension of stones and ice in the water

1. The total volume of stones and ice is equal to the volume of drained water;

2. The total gravity of stones and ice is equal to buoyancy, and the total mass is equal to the mass of the water discharged.

If the water surface rises by 6 cm, the volume of the water discharged is 100 cm 6 cm = 600 cm and the mass is 600 g.

V stone + V ice = 600cm

Stone v Stone + Ice V Ice = 600g

When the water level drops again, the volume of water after the ice cube turns into water is 100 cm less than the volume of the original ice, from which the third equation can be listed.

v Ice - Ice v Ice Water = 56cm

From the equation v ice = 560 cm

Bring in the V stone = 40cm

Bring V Ice and V Stone into the Obtainable Stone =

Idea: To figure out the meaning of the problem, it is best to draw a diagram and then list the equations.

It's very easy to get a relational formula.

V stone V ice = 600 cm cube.

V stone V water = 544 cm cubic.

m ice = m water.

You can solve the equation and it should come out.

Let the density of the stone block be 1 and the volume be v1. The volume of the ice cube is v2. According to Archimedes' principle ( 1v1 The volume of ice and stones is the same as the volume of water discharged: v1 v2 = 6 100 10 -6, when the ice is turned into water, the volume decreases, so v1 v2.

Combining the above three equations gives us 1=

1.When the temperature control switch S0 is disconnected, the water dispenser is in a state of heat preservation.

At this time, the electric power of the water dispenser p1 = u r1 = (220v) 1210 = 40w

2. R1R2 is connected in parallel when heating, P2=U R2=(220V) 100=484W

Total power p = p1 + p2 = 40w + 484w = 524ww = pt = 524w * (5 * 60s) = 157200jq suction = cm (t-t0) =

The efficiency of the water dispenser in converting electrical energy into water = Q suction w = 126000j 157200j = 80%.