In the second year of junior high school physics questions, the master is coming this way

Because the total weight of the iron, people, and ship exceeded the displacement of the ship, and the time for two trips was not enough, the way to consider reducing the load was to put the iron in the water and the ship to drag it away. Can it be implemented? Let's verify first, consider the extreme case, that is, all the iron is put into the water, and the load is the least at this time, that is, 65*, and then consider the critical value.

That is, put a part of the iron in the water, and the weight of the ship is less than or equal to the maximum displacement. Suppose the iron on the ship is x tons, and the iron in the water is (65-x), and the weight of the ship on the iron in the water is (65-x)-(65-x) that is, the weight of the iron minus the buoyancy exerted), plus the remaining iron and the human ship, i.e., (65-x), to get x

The answer is that the ship is loaded with less than a ton of iron, and the rest is dragged by the boat, and the transportation is completed in one trip.

Hope...

I don't understand, the displacement minus the human ship 80t-17t = 63t, the ship can carry up to 63 tons, if you run two times for 24 hours, you can't complete it within 20 hours.

Unless there are two boats.

According to the title, the ship is 80 10 = 8 hours one way from A to B, 24 hours for two trips, and the maximum loading time is 80-17 = 63 tons per load.

The actual requirement to send 65 tons of steel within 20 hours shows that it must be transported at one time.

If x tons of steel are loaded, and the remaining 65-x tons of steel are sunk in the water and towed by the ship, the following relationship must be met:

65-x)-(65-x)/<=63

where: [(65-x)-(65-x) is the bearing capacity exerted by the steel submerged in water to the ship, and (65-x) is the displacement tonnage (i.e., buoyancy) of the steel in the water

By calculation: x<=tons.

That is, the ship is loaded with no more than a ton of cargo, and the rest is sunk in the water and dragged and transported by the ship.

Are you going with the current or against the current? This is important. And now the questions in the second year of junior high school are so difficult?

The diameter of the oil molecule is about meters.

v = 192 10 6 dm = liters.

liters of oil.

1.According to the tone, this is what our teacher said. The second is timbre (the specific teacher has not yet spoken) 2The density is high (I don't know how to pinch this myself, but I look at the first floor) 3Solution:

v=340m/s

t=s=vt=340m/s×

A: ......4.(1) It cannot be heard, (2) Because the vacuum cannot transmit sound, there is no medium, and (3) It is also possible to use the radio to talk.

1。According to the tone of the voice, the tone of the empty is high, and the tone of the real is low.

2。High density.

3。Let the speed be x, and the sum of the distance traveled by the sound in seconds plus the distance traveled by him in seconds is equal to twice the amount of distance traveled by the sound in seconds, x=

4.No, there is a vacuum in space, and there is no medium for the transmission of sound. So you can't hear each other's voices. It is possible to talk wirelessly**.

1.The pitch is high or low.

The sound of ripe is more muffled.

2.The higher the density, the better the sound insulation.

3.Solution: Let the speed of the vehicle be xm s

Obtained by S vt.

After the car is gone.

Sonic is gone (450*.)

The title suggests that it is 450*

Solution: x=20m s

A: The speed of the vehicle is 20m s

4.Can't be heard.

Because the transmission of sound requires a medium, space is in a vacuum, and the vacuum cannot transmit sound.

Procedure: Converse via radio.

1. The sound of "Dongdong" or "Dede" of hitting the plank is not.

Symbol of cooked; The sound is tired and turbid, similar to the sound of "Bubu" of the drum and the sound of vibration, which is ripe enough The standard melon has more water content and the melon body is heavier; Ripe melon, because the flesh of the melon is thin and crispy, the tissue is relaxed, and the body.

It is lighter than raw melon.

2. High density. 3 No, air cannot travel in a vacuum, whereas space is vacuum. With radio, no medium is required for the transmission of radio signals.

1. According to the timbre of the watermelon.

2. High density.

3. Let the speed of the car be x450 340 + (450-x) 340 = solution x = 50 and the speed of the car is 50m s

4.I can't hear it, because space is a vacuum, and if there is no sound in the vacuum, you can use radio to communicate.

For the first question, we know that the density of water is that the density of water is 1g cm 3, which is 1*10 3kg m 3. In the title, it is said that the depth of the wooden block immersed in water is 5cm, and the area of one face of the cuboid can be obtained by the buoyancy formula f float = v row * water * g, and the buoyancy in the water is equal to gravity, 16n = h * s * water * g =. Then in another liquid, the same buoyancy formula f floats = v row * water * g has, 16n = h * s * liquid * g = liquid * 10, and the liquid = is obtained.

Or use the formula buoyancy to provide support force, buoyancy is proportional to the volume and density of the liquid, the buoyancy is unchanged, the depth and density are inversely proportional, so the density of the liquid is the density of water liquid =.

For the second question, (1) we know from the question that the density of ice is smaller than the density of salt water, from the knowledge of junior high school, we can know that the ice is in a floating state in the salt water before melting, from f float = v row * * g, v = 20 cm 2, then the indicator of the graduated cylinder should be 70 cm 2.

2) After the ice melts, it becomes 21g of water, plus the original salt water, the total weight does not change, but the density is smaller, and the unknown number is larger than 70. From the comparison of the results of the first and second questions, it can be found that the sea level will inevitably rise after the iceberg melts, so we should pay attention to protecting the environment and reducing greenhouse gas emissions.

1. Buoyancy provides support, buoyancy is proportional to the volume and density of the liquid, the welfare remains unchanged, and the depth and density are inversely proportional, so the liquid density is a must-read for doubling the water.

2. a. Ice-water mixture, the indication is (21+

b. The indicator becomes unknown, but it is greater than the original indicator 70, because the density is less than but the total mass remains the same, and the iceberg is found to melt and the sea level rises.

According to Ohm's law, r=u i

The resistance is 10 ohms. To want 1A, the voltage should be 10V

The resistance does not change with voltage, so it is still 10 ohms.