How to do this junior high school physics problem? 15

Ohm's law: i=u r u=ir r=u i

Series circuit: i is the same everywhere r=r1+r2 u=u1+u2 r1:r2=u1:u2

u1=i1r1 u2=i2r2 u1:u2=i1r1:i2r2 i1=i2 so u1:u2=r1:r2

Parallel circuit: U is the same i1:i2=r2:r1 i=i1+i2 1 r=1 r1+1 r2

u1=i1r1 u2=i2r2 u1 u2, so i1r1 i2r2 i1:i2=r2:r1

Hope it helps.

**It's too blurry, I can't see it clearly, and there's a picture in the wrong direction, so I can't see it clearly.

1. The power of Xiaoli's work.

w=fs=250n*2*6m=3000j

So the power is: P=W T=3000J 10S=300W2 mechanical efficiency of the pulley.

gh fs=(250*2-50)*6 3000=90%3If the mass of the object is m, the pulley block is used to improve the object, and the expression of the mechanical efficiency of the pulley block and m is obtained.

[m/(m+50)]*100%

1.Xiaoli does work w total = fs = 250 * 2 * 6 = 3000J, power p = w total t = 3000 10 = 300W

Extra = g dynamic h = 50 * 6 = 300j, w useful = w total -w extra = 3000-300 = 2700j

Mechanical efficiency = w useful w total = 2700 3000 = 90% 3=w useful w total = mgh (mgh + m dynamic gh) = m (m + m moving).

(1) Wind power transmission * duration =

2) The difference between the value of the energy meter in 30 minutes is.

3) A total of 20 minutes of refrigeration within 30 minutes, 10 minutes of air supply, the electric energy used for refrigeration is the result of the first two questions), then the electric energy consumed by refrigeration is divided by the refrigeration time, that is, the unit of electric power is kw).

Note: The time should be in hours.

Solution: According to the title, within 30 minutes, the air conditioner refrigeration and air supply cycle 2 times and 10 minutes of air supply consume electric energy w=pt=

30 minutes of electric energy representation change, that is, at this time the air conditioner consumes total electric energy within 30 minutes of air supply 2 times consumption of electric energy = , then the total refrigeration consumption of electric energy w = Chen Yuchao 2009 for you to answer, I wish you learning and progress If you agree with my answer, please click the [Accept as satisfactory answer] button in time The mobile phone questioner can comment on the client "satisfied" Your adoption is the driving force for me to move forward

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I don't know, I don't know, I don't know, I don't know, I don't know.

(1) The heat released by the complete combustion of gasoline: q discharge = qm =, the power consumed by gasoline p1 = q t =

2) 72km h=20m s, 10min=600s, the distance that the car passes within 10min s=vt=20*600=12000m

The work done by the traction of the car within 10min w=fs=

The power of the car traction is made p2=w t=

3) It was found that the power of the car's traction work was less than the power consumed The reasons include: gasoline is not completely burned; Exhaust gases take away part of the heat; Loss of a part of the energy due to heat transfer; Overcoming friction consumes a part of the energy, etc.).

1) Power consumption p1 = mq t = [Note: (7) represents the 7th power, please change it by yourself].

2) Traction power p=fs t=fv=

3) Only a small part of the heat burned by gasoline is used to tow the car to do work, and most of the power consumption is lost.

Reasons:1Power loss between the mechanical transmission of the car2Friction between the car and the road surface is lost in heat.

（1）（2）p=

3) A car exhaust gas takes away a lot of energy, b the car overcomes frictional resistance and consumes a lot of energy.

p = r²v × v² /2= πr²v³ /2

In ...The measures that can be taken to accommodate the negotiation are:Increase the length of the blades of the wind turbine. Bi Li

1. The total volume v=m p=89kg (

1mm^2=(1mm)^2=(1*10^-2dm)^2=1*10^-4dm^2

Cross-sectional area s=25mm2=25*10 -4dm 2Lengthl=vS=10dm (25*10 -4dm2)=4*10 3dm=400m

It is known from density = mass divided by volume, volume = mass divided by density = 89kg to the power of 3 = 1 10 negative quadratic m

From volume = base area height (that is, length) to know height = volume base area = negative power of 1 10 25 minus 9 power of 10 = sixth power m

v=m =89 8900=m³ l=v s=. The answer can't be 400m.

m=ρ×s×l。where m is the mass, is the density, s is the cross-sectional area, and l is the length. Do the math yourself. Note that the cross-sectional area should be converted to m first. The square should be 10 -6.

You first distinguish whether it is copper or steel