Three physics questions for the sophomore and three physics questions for the first year of high sch

1) r=p*l is the resistivity, l length, s cross-sectional area. l=60cm=cross-sectional area s=. Resistivity p copper =, p aluminum =.

r copper = p*l s = ohm.

r Aluminum = p*l S = Ω.

In the experiment, the circuit length is short, the current is small, the wire resistance is small, and the loss error is small. The transmission line is a long distance, with high resistance, high current, and high power loss, so it must be considered.

2) Two R's in parallel, and then one R in series, that is.

Diagram: 3 --r --2 (r r) --1

r12= r23=r r13=

3) r=p*l s=ohm.

Voltage u=ir=400*, this is called step voltage.

Hope it helps!

I'm a senior in high school.

1.In the textbook of the second year of high school, there are values for the resistivity of copper and aluminum, which can be calculated according to the formula r=pl s.

2 No picture. 3.Same as 1

Are you studying physics?

This is the unit summary question on the textbook, you can buy the reference material for the detailed explanation of this textbook, which is very detailed! I'm too lazy to type for you.

1) The formula is r=p*l sWhat to pay attention to in this question is the unit. 60 cm = cross-section = squared.

In short, the square millimeter is converted to a square meter, which is divided by 10,000Because thinking too much about doing experiments will only make experiments difficult, and we want the essence of experiments. Whereas, power lines are long-distance.

As can be seen from the formula, the longer the l, the greater the resistance, so there will be electrical loss, so it must be considered.

2) If you don't give me a picture, it's very difficult.

3) r=p*ls=resistance.

Voltage u=ir=400*

Do you still ask such a simple question?

1.The horizontal force is balanced, and the wind force = the horizontal component of the rope tension force = FCOS 60° = 40 * 1 2 = 20N, which is crossed and crossed, which may be that the steps of the problem are not standardized.

2.It's to take into account the different directions of friction, and you think about it very closely.

3.Look at this answer.

To supplement the upstairs, in question 2, it is said that the object moves at a uniform speed, and it is necessary to consider whether it moves at a uniform speed upward along the inclined surface or along the inclined downward direction, and the direction of sliding friction is different. However, as the title describes: "Under the action of the upward tensile force f parallel to the inclined plane, the inclined plane moves at a uniform speed along the inclined plane with an inclination angle of 37°", it generally refers to the upward motion along the inclined plane, and the direction of the sliding friction force is opposite to the direction of the relative motion, so it should not need to be discussed.

Because the work done by friction is constant, e2=2fs-fs, e1=fs-fs, therefore, e2>2e1

2，v=w(r+r)

Multiply by the root number (3g 2h).

T1--T2 has a small current at all times.

The resistance is increased.

Therefore the pressure decreases, it is weightless, and it accelerates downward.

T2--T3 is a uniform descent process.

T3-T4 is overweight, i.e., there is an upward acceleration that is manifested as a downward deceleration process.

Therefore c is correct.

If the pressure increases, the resistance becomes smaller, and the current becomes larger, so according to the diagram analysis, the pressure has a process of going from gravity to less gravity, and then returning to gravity, and then greater than gravity, and then returning to gravity.

So choose D

2, yes, the size of the train is compared to the distance from Beijing to Shanghai, and it can be regarded as a quality point.

3,15min, the ship's water speed is unchanged, with water as a reference, the falling items are equal to not moving, driving for 15 minutes, and then spending another 15 minutes to turn back.

4. I can't see all the questions.

aThe magnitude of the sliding friction force on the ground ff= n=

The magnitude of the tension t of the rope to b t=u*20 n

The magnitude of the horizontal force f is f= +u*20 n=

It seems that B is tied to a vertical wall with a horizontal rope, otherwise it would not have been possible.

A 60 N to the ground, so 24 N to rub.

B against A20 N, the friction is 8 N, so t = 8 N.

f is the sum of the friction between t and a against the ground, which is 32 N.

This problem itself has a problem, only by knowing the pressure of b acting on a can the first problem be calculated, and the tensile t required in the second problem is the same problem, this t does not know that the first problem cannot be calculated.

The first step is to use a scale to measure the height of the diagram of the desktop Punzhaoqiao, so as to find the scale corresponding to the diagram, for example, by measuring the height of the desktop shown in the diagram is 4 cm, the scale is meters, that is, according to the size in the figure, there is no 1 cm to represent the actual height of the meter.

In the second part, the distance of OA and OB is measured with a scale, and the actual distance from A and B to O is multiplied by meters.

The third step is to show positive and negative, point B is positive, and point A is negative.