Ask a physics problem detailed process .

is two-fifths of the new volume, so it is (1-2 5)*(2 5)=6 25

p(wood)vg=3 5p(water)vg The result is independent of volume or 2 5

The second outcropping volume is vThe first f1 = p1v1 = (p0) (3v1 5) g (the density of the p1 block, the volume of the v1 block, the density of the water at p0, 3v1 5 is the volume immersed in the water) the second f = p1v2 = p0 (v2-v) g (v2 truncates the volume left by the part that is exposed to the water) v=6v1 25

Apply Gauss's theorem and electric potential.

First take a piece of area s on the plastic sheet, because the flat plate is large enough, approximate an infinite plane, determined according to the symmetry:

1) The direction of the electric field is perpendicular to the plate, and the direction is the same;

2) The plastic sheet goes up and down into the space of the metal plate, and there are: e1, e2 are equal in size at each point.

3) According to Gauss's theorem, there is (e1 + e2) s = se1 + e2 =

Then, according to the electric potential, the upper and lower metal plates connected by the wires are taken as the zero point of potential energy, and the same electric potential u is on the plastic sheet

u = e1 * d /3 = 2 e2 * d/3e1 = 2 e2

e1 = 2σ/3ε

e2 = σ/3ε

A uses the ground as the reference system, and the book has an upward initial velocity after sliding, so it is believed that the book rises first and then falls.

B uses the elevator as the frame of reference, and in this frame of reference, the initial velocity of the book is zero when it falls, so it is considered that the book falls directly.

So choose D

Answer: d

Analysis: bai

Select du different references, the motion of the object.

The zhi state may not be the same, which is the relative of motion and special rest.

Therefore, AB is one-sided.

If we take the elevator as a reference, the elevator is equivalent to "stationary", and the book in the hand will fall directly to the ground just like a person standing on the ground and falling. That is, the answer is d.

If you take the ground as a reference, because the elevator is rising, and the book is also rising, at this time, the book is falling, and the people on the ground look at it, which is equivalent to an object falling off on the balloon that is rising, and the object will move up for a short time and then fall down due to inertia. Therefore, A is analyzed with reference to the ground.

I don't know what to ask.

Leaving the book in hand, bai takes the ground as a reference, and it has an upward initial dao with the elevator du

Speed so it's movement.

Back yes - first up and then down answer c wrong. Take the elevator as a reference to its initial velocity of 0, and after leaving the hand, it falls directly d correctly. Therefore, the reference is different, and the movement is also different, and a b uses the word "only", then ab is wrong.

The title has already explained that different reference systems have been chosen, A uses the earth as the reference system, and the book rises first and then descends; B uses the elevator as the reference system, and the book is in free fall, choose D

d If the ground is used as a reference, the book will first rise a certain distance and then fall due to inertia, if the person and the elevator are used as the reference, the book is undoubtedly directly falling, so A is based on the ground as a reference, and B is based on the elevator as a reference, so D is chosen

D, when the book falls, the speed is the same as the elevator, so choose D

Note: Taking the building as a reference, it rises first and then falls, because the book has an upward velocity when it falls, and it has to move upwards for a distance before falling.

D, with different objects as the frame of reference, the state of motion is different.

Sound t = s (distance) c (speed of sound) = 1000km seconds = 50 minutes train (take the fastest train as an example) v (the fastest speed of 380km h will be launched soon, the average speed will be 250km h).

t = s (distance) v (train) = 1000km 250km h = 4 hours jet airliner v (airplane) average speed 984km ht = s (distance) v (airplane) = 1000km 984km h = 1 hour.

The sound speed is 340m s, and the time from Shanghai to Beijing is 1000000 340 = 2941s = hours.

The train is 80km hours and it takes about 1000 80= hours to get from Beijing to Shanghai.

A jumbo jet is 900km an hour, and it takes about 1000 900= hours to travel from Beijing to Shanghai.

Because the speed of sound propagation in the air is 340m s, and the distance from Beijing to Shanghai is 1000000m, the time t=1000000 340=;

The speed of the jet is 600km h, which is converted to v=600*10 36=

Known: s=810km t1=19:30 t2=22:30

Solution: v=s t=s t2-t1=810 Answer: The average speed of the modified car is 270km h.

The absolute standard answer, we've just talked about it.

810km/3h=270km/h

Remember: the average speed, regardless of whether you stop, accelerate, or average speed, is only a conceptual "average speed", so divide the total distance by the time it takes!

Equations can be listed according to the title:

Solving the system of equations yields: v=1m s

n=70 So the speed of the escalator movement is 1m s, and the number of customers on this escalator is 70.

Each car consumes fuel every year, and the average efficiency of the car's internal combustion engine is 30 percent, and its effective usage is m=

Increasing the efficiency of the internal combustion engine by one percent will result in annual fuel consumption of m'= Savings per car is m=

The total savings of 1 billion vehicles is m=

10* billion tons.

The reduction of waste is the saving.

Car fuel consumption = 10 9

Fuel savings = 10 9

How many cubic meters of oil is 70000000L?

70000000l 1000l m3=70000m370000m3How many kilograms of oil?

70000m3*900kg m3=63000000kg63000000kgOil combustion value?

44000000j/kg*63000000kg=2772000000000000j

First of all, 1m = 100L 70000000L = 70000m mass is 70000x900 = 63000000kg, and the energy released is 63000000kgx440000000=2772000000000000j