Solve a junior high school physics problem, solve a junior high school physics problem

At the beginning, both the car and the plane are stationary, but due to the inertia of the aircraft, after the car starts, the aircraft will still maintain its original state of motion, that is, the stationary state. So there is a relative velocity between the plane and the car, and the speed of the car is greater than the speed of the airplane, so the plane crashes into the back of the car's cabin.

Because the bus is in motion and the plane is stationary in a space, it is the car that moves and not the plane that moves, so the plane hits the back box, and also, you can't play with the plane on the bus.

It is the reason for the relative motion, the plane and the car are stationary at the beginning, and the relative velocity is 0, but when the car starts, the relative velocity of the plane and the car suddenly does not belong to 0, so the relative displacement occurs, so it collides.

The plane does not come into contact with the car. It's quite the same as ***. The car starts. The car has a speed forward. And the plane has no speed. So the plane crashed into the back of the compartment.

The speed of the plane should have been the same as that of the car, but when the car suddenly accelerated, the plane moved backwards relative to the car, so it hit the rear compartment.

The car drove away. You need the air around you to fill the parking space. So I sucked the plane in. Due to inertia. I just crashed into it.

Relative stationary versus motion problems.

Originally, the car didn't move, and the plane didn't move, and both velocities were 0, and then the car moved, and there was a v, and the plane's horizontal velocity was still 0, so it crashed.

1. Cars and small planes turned out to be stationary.

2. The car starts suddenly.

3. Due to the inertia, the small aircraft still stays in place (stationary).

So the plane crashed into the back of the car

According to the meaning of the title, it can be seen that the pressure of the three liquids on the bottom of the container is equal. In this case, the pressure of the liquid on the bottom of the container is not necessarily equal to the gravitational force of the liquid due to the different shapes of the containers containing the liquid.

According to the pressure formula: pressure f p s, while the force area s is the same. So the pressure of the three liquids on the bottom of the container is equal. The answers of A and B are wrong.

Container containing alcohol, the pressure of alcohol on the bottom of the container f the gravity of alcohol g1.

The container containing water, the pressure of water on the bottom of the container f the gravity of the water g2.

Container with brine, the pressure of the brine on the bottom of the vessel f the gravity of the brine g3.

Since the pressure of the three liquids on the bottom of the container is equal, g2 g1 g3.

Answer: C is correct.

Note: Although containers of different shapes are placed on a horizontal tabletop, only the pressure f of the liquid on the bottom of the container in the diagram A is equal to the gravitational force g of the liquid in the container. And B plot f g, C plot f rotten Lu g.

<>Since the pressure is equal, the state impulse gravity of the cylindrical part is equal, the volume of brine is less than that of the cylindrical part, the volume of water is greater than that of the cylindrical part, and the volume of alcohol is equal to the cylindrical part, and the cylindrical part is closed by the fraction as shown in red), so the mass of the brine is the smallest, and the answer is option c.

When connected in parallel, the total current is equal to the sum of the currents of each parallel part, > "For example, in the figure above, two bulbs are connected in parallel, and the ammeter measures the current of the bulb below.

<>This is a typical ammeter for measuring the dry current of a parallel circuit.

b correct. When heating, evaporation occurs when the temperature of the water in the container rises, and the temperature of the gas in the sealed container also rises, so that the air pressure above the water surface in the window increases, which is greater than the air pressure on the water surface of the test tube, and the air pressure above the water surface in the test tube is still an atmospheric pressure; Therefore, the boiling point of the water in the container is higher than the boiling point of the water in the test tube; Therefore, the water in the test tube boils first.

Thank you for adopting.

From the analysis, it can be seen that the pressure difference between the internal and external pressure is equal to the gravity i.e., f=g=

It can be seen from the pressure formula p=f s.

p=g/ss=π x r x r

Substitution data for solving.

p = Pa (rounded).

Let the air pressure difference be p, then:

The pressure exerted by acting on the surface according to the difference in air pressure = the gravitational force p x ( x r x r) = g of the square plate

Solve: p= 1777 Pa.

Being able to absorb the glass plate means that the pressure difference = gravity, do the math yourself, the answer should be.

f suction = g because f = atmospheric pressure minus suction cup pressure.

s(po-p) =f, then po-p=g s=

Solution: Let the mass of this pot of water be m water, δt=97 -27 =70 according to the formula q=cmδt, and the heat required to heat the water.

Q absorbs = m water c water δt = 294000m water (j) is obtained by the formula p = U2 R.

The resistance of the electric kettle r pot = u amount 2 p amount = 220v 2 1100w = 44 Therefore, when you real = 198V, p real = u real 2 r pot = 891w (it can also be based on the power relationship of the same electrical appliance at different voltages p amount p real = u amount 2 u real 2).

From the formula w=pt, heating this pot of water consumes electricity.

W total = p real t = 891w 7 60s = 374220j In summary, the heating efficiency of the electric kettle.

Q Suction W total = 29400m water 374220J water.

So from the calculation process, it can be seen that you definitely have the conditions not to write it all, either the quality of this pot of water, or the volume of this kettle.

Personally, I think you should have underwritten the capacity (volume) of the kettle

If there is, the process of asking for water should be added to the top.

From the formula m= v, the mass of this pot of water is .

m water = water v water = forget it yourself.

The problem lacks one condition: the mass of the water m (or the volume of the pot).

U 198 Volts, U 220 Volts, P 1100 W, T1 27 degrees Celsius, T2 97 degrees Celsius, T 7 minutes 420 seconds.

cWater joules (kilograms Celsius).

Analysis: In the heating process, the electrical energy used is e electricity (u 2 r)t (u u forehead) 2 * p forehead * t

Get e-electricity (198 220) 2 * 1100 * 420 374220 joules.

During this time, the heat absorbed by the water is q c water * m * t2 t1) If the quality of the water m can be known from the above equation, then the heating efficiency obtained is q e electricity.

There should be a condition missing in this question, that is, the quality of this pot of water, which should be told.

Suppose the mass of this pot of water is m, heat it from 27 to 97 and need to absorb the heat q=cm(t2-t1), c is the specific heat capacity of the water, constant, t2=97, t1=27, bring in the data, you can find q

According to the nameplate of the electric kettle, the resistance of the electric kettle can be calculated r=u p=44, when the actual voltage is 198v, the actual power of the kettle is p=u r=(198v) 44 =891w, and the total heat q released for 7min of work q total = pt=891w 7 60s = 374220j

then heating efficiency = q q total.

q is the amount of heat absorbed by the water as previously calculated.

1) Since the return capsule falls at a constant speed, the air resistance f = gravity g of the return capsule = mass m * gravitational acceleration g of the return capsule, i.e. f = mg;

2) As can be seen from the question, the air resistance f = the square * proportional coefficient k of the velocity v of the return capsule, that is, f = v 2 * k;

Substituting equation (1) into equation (2) obtains, mg=v 2*k, from which we can see that the square root of the falling velocity v = mg k of the return capsule.

No water has volume or mass, it is impossible to find!

Is there no capacity for the kettle?

What about the quality of the water in the kettle?

It must be the choice of B.

Are you a human-taught version of the physics textbook [we are], if so, then on page 7 there is the following original words:

At the beginning of the 20th century, scientists discovered that the structure of the atom is very similar to that of the solar system, its center is the nucleus, and around the nucleus, a certain number of electrons are moving around the nucleus.

Hope it helps, o( ohehe.