Ask a few physics short answer questions and ask two physics short answer questions

1. Reverse direction.

Because the acceleration of people and vehicles should be equal.

So the bottom of the car gives a forward static friction.

And the upper body of the person is not forced, so it falls backwards.

2. When the train comes, due to the fast speed, a small density area will be formed near the train.

Behind the person is a standard atmosphere.

So it's easy to hit the train, so stand outside the safety line.

3. In the water, the deeper the place, the greater the pressure.

Current technology does not allow submarines to dive to infinite depths.

So the depth of the dive is limited.

1.Reverse the direction of travel. Because people have inertia, the car moves people's inertia, so that people have a tendency to remain relatively stationary with the ground, so they fall in the opposite direction of travel.

2.Because when the train (subway) is running, it drives the surrounding air to follow the high-speed operation, and the air pressure of the high-speed airflow is less than the stationary airflow, and this air pressure difference will push people who are very close to the car onto the car, causing danger.

3.Because the deeper the water pressure, the greater the submarine, the submarine can not withstand too much pressure, and will be crushed and deformed.

1.will lean in the opposite direction. When the car is stationary, the person and the car remain stationary, when the car starts, the car begins to move, and the person still has to remain stationary due to inertia, so it will be opposite to the direction of the car.

2 .The pressure of the place where the fluid flow rate is large is small, when the train passes rapidly, it will drive the surrounding air to do high-speed movement, it is close to the train at a certain distance of the pressure is small and the pressure from the outside, if people stand within the distance, they will be pushed to the train because of the atmospheric pressure of the outside world, and the danger occurs, so a one-meter line should be set up. 3.

According to the pressure = density * g * depth, the further the submarine dives, the deeper the depth, when the density and g are constant, the depth and pressure are proportional, the greater the pressure and the excessive sinking will flatten the submarine.

1. Falling in the opposite direction to the direction in which the car is heading, this is inertia (because he was standing still at the beginning, inertia is to try to maintain his original speed).

2. Because the train will drive the surrounding air to run at high speed when it passes, the air pressure of the high-speed airflow is less than that of the stationary airflow, and this air pressure difference may roll the people in the safety line into the rapid train, resulting in collision injuries.

3. Because the deeper you go, the greater the water pressure, and the strong water pressure will squeeze the submarine out.

1 post. Because people have inertia.

2. The pressure of the gas is small in the place where the flow velocity is large, and the speed of the train is great when it is moving, and the flow velocity of the air around it is also large. If it is within the safety line, it is easy to cause accidents.

3. The pressure inside the liquid increases with the increase of the depth of the liquid, and the submarine has the maximum pressure value to withstand. So you can't dive indefinitely.

1。The fuse should have a high resistance and a low melting point!

If the resistance is thicker, the resistance will be smaller, so pinch a hole to make it slender, so that the resistance can be larger.

2。Circuit diagram Draw 2 resistors in series, and 2 resistors in parallel!

Not contradictory! When boiling water in an electric furnace, the wire and the electric furnace wire are connected in series, and the current is the same, according to q=i 2rt, it can be seen that the resistance is large, and the heat is generated.

When two electric furnaces with different resistances are connected to the home circuit, the two electric furnaces are connected in parallel according to q=(u 2 r)t

It can be seen that the less resistive power generates more heat.

The cause of this twice is resistance. (1) It is the same voltage, the resistance is different, and p before = u 2 r small p after p = u 2 r large.

Before p is greater than after p it is not easy to protect the circuit (2) The electric furnace wire and the connected wire are connected in series, and the current is equal According to o = i2 r t, it can be seen that the wire resistance is much smaller than the electric furnace wire resistance, and the wire resistance produces less heat at the same time, and the electric furnace wire resistance produces more heat. As a result, the wire of the electric furnace is hot and red, while the wires connected to it barely generate heat. I won't talk about the specific experiments later.

The second should be that everyone's constraints are different. Xiao Ming's situation is the same as the current, so the resistance is large and the heat is large. Second, when the voltage of the circuit is equal, in fact, the consumption of the two electric furnaces is different, and the consumption of the small resistance is large, which can be seen from p=u 2 r

1.The force f=4000*10*speed of the car on the inclined plane is to reach the rated output power p=fv when the maximum speed is reached

v=p/f=10m/s

The maximum speed is that the traction force is equal to the drag, and the traction force is also 6000n2The rated power of the truck p=fv=2000N*2m s=4000w, the slope is stressed, f1=f+mgsin30=7000NV1=p=The speed of the landlord is not wrong???

The maximum speed is when the friction is equal to the traction...

When the switch is closed, the circuit enters the working state. As the resistance of the rheostat connected to the grip increases, the voltage distributed to the resistor increases under the characteristics of the series circuit, and the value displayed by the voltmeter also increases.