A junior high school physics question about pulleys

As shown in the figure, the movable pulley is directly connected to it by two sections of rope, the middle section of the rope and the right section of the rope are upward on the moving pulley, and the upward pull force of each section of rope on the weight (pulley weight is not counted) is f, so 2f=g.

Note: It is the upward pull of the rope experienced by the movable pulley, not the downward pull of the rope on the fixed pulley. You draw upward arrows on the ropes on either side of the moving pulley and you're good to go.

The two sections of rope in contact with the movable pulley bear the weight of the object and the pulley together, and of course the friction, and theoretically the free end of the rope is equal to one and a half of the above.

Total gravity g = 200 + 600 + 40 = 840n

The movable pulley, the man, and the frame are considered as a whole, connected to three ropes, and each rope has equal pulling force. So gravity is borne by a total of 3 strands of rope. f=g 3=280nUnderstood?

Draw a line from the middle, and the fixed pulley is equivalent to three strands of rope to bear, then the calculation is:

200n+600n+40n)/3=280n

It must be three strands, with the middle of the two pulleys as the boundary, there are three sections on the upper pulley, so there are three forces in total. That's another way of saying it in your resource book. Force analysis, (200 + 40 + 600) 3, can be. Because the fixed pulley itself is balanced by force, it is not counted.

Because the rope also gives people a pulling force, which relieves the pressure on the floor.

It is obtained by g=mg=vg.

g Fe = 7900*

g aluminium = 2700*

The pulling force of each strand of rope is equal to the gravitational force of aluminum27n

For movable pulleys and iron blocks, the upward force is 27N*2=54N, and the downward force is 10N+79N=89N

The net force is 89n-54n=35n

So the pressure of the iron block on the ground is 35n

The area is 10cm*10cm=100 square centimeters = square meters pressure p = f s = 35n square meters = 3500n square meters 3500pac The answer is that the unit is a unit of density, not a unit of pressure.

Please click to adopt, if you are not sure, you can ask questions.

Aluminum block gravity =

The upward pulling force received by the pulley is 27*2=54n

The upward pulling force received by the iron block is 54-10=44n

Gravity of the iron =

The pressure received on the ground is 78-44=34N

Pressure = 34n

v = 10 = 1000cm = 1 dm , iron = decim , aluminum = decimeter g aluminum = m aluminum g = aluminum vg =, g iron = 78n, g wheel = 10n rope tension t = g aluminum = 27n

For movable pulleys: 2t = F iron + G wheel.

F iron = 2t-g wheel = 2 * 27-10 = 44n

For the iron block:

F pull = f iron = 44n

Pressure on the ground f=g, iron-fpull=78-44=34n, compacted area, s=10*10=100cm=

Ground pressure p=f s=34

In fact, there is an easy way to do this, which is "odd and even". That is to say, if n is an odd number, start with the moving pulley, and if it is an even number, start with the fixed pulley. And the n 5 you gave is an odd number, directly from the moving pulley to start drawing, there are 5 lines in the picture to hang the moving pulley, so n 5, I hope it can help you, thank you!

Start connecting with the hook of the moving pulley. Connect 5 movable pulleys.

Because odd and even, and because 5 is an odd number, start drawing from the moving pulley.

1) The pulling force of the pulley on object B is equal to the pressure of the object on the ground.

Therefore: f pull = ps = 2 * 10 4 *

2) Fb*ob=Fa*OA is obtained from the principle of lever balance (FB and FA represent the tensile force at the B end and the tensile force at the A end, and A, B should be reduced).

And because fa=ga=10n, fb=2*10 1=20n, then analyze the pulley on the left, f left + f middle + fb = g pulley + (g b - f pull) and f left = f middle = fb

8g pulley = g B.

So g pulley = 10n

g B = 80n

Now add another C under A, and the pressure is 0, then push back 3FB=G pulley + G B=90, so FB=30N

Then from the principle of leverage equilibrium, fb*ob=fa*oa, then fa=30 2=15n

So g C = fa-g A = 15-10 = 5n

1) The pressure is equal to the pressure divided by the surface area p=f s

The pressure on the ground is p, and the area is s, then the ground has a support force of 3*10 to the 4th power. （3*104）

Let the weight of g be 1 8g by the principle of lever balance to obtain fb*ob=fa*oa (fb, fa is to represent the pull force of the b end, the pull force of the a end) the pulling force of a to a is 10n, then the pulling force of b to the rope is 20n, and the pulling force of the three ropes to the pulley is 60n

9/8)g=60n+30n=90n

Launch g = 80 n g pulley = 10 n

At this time, the tensile force f of the movable pulley on object B is 80N-30N=50N, and the pressure is exactly zero, and the tensile force without the rope should be 90N, 3 =30N, then FB2=30N, Fa2=5N, so GC, is equal to 5N

1) From the gravity of A, the tensile force of the rope at the end of B is known to be 20N, and the moving pulley and the object B as a whole are analyzed, the gravity of the 9g wheel (B and the movable pulley) and the tensile force of the three-strand rope supporting force are 60N, and the supporting force is equal to ps=3 10 4N (suspect that there is a problem with the data), so as to calculate the G wheel = 3340N (guess that the most likely is 10N, the following is calculated with 10N), and then analyze the movable pulley separately, and the gravity, three tensile forces and B's tensile force on it, list the balance formula, and calculate f=50N

2) List the equilibrium formula 3 (G C + G A) = G B + G wheel (G B = 8G wheel = 80N), so G C = 20N

Pulley and lever principle.

All ropes on the pulley are equal in magnitude, and the rest depends on other people's answers.

Look at the number of strands of the moving pulley rope.

Apparently this one has 3 shares.

So the pulling force is (500+10) 6=85N.

6 6 = 1 meter.

Fainting, g matter = 500n f = (g matter + g motion) 3 = 510 3 h = 2m

If the direction of the pull is the same as the direction in which the object rises, the number of ropes is counted.

If the direction of the pull is inconsistent with the direction of the object's rise, then subtract the total number of strands of the rope by 1, don't look at the following.

It's a very simple question, and I loved it when I was in junior high school.

Look at the ** number is mainly to see that there are a few ropes on the moving pulley to pull it, like this question, it looks like three strands.

Analysis: The number of ropes that bear the moving pulley by the formula f = (weight of the moving pulley + weight of the object). As can be seen from the diagram, there are three ropes that bear the movable pulley, so f=(500+10) 3=170N.

The distance the weight moves = the distance traveled by the free end of the rope The number of ropes that bear the movable pulley. So 6 3 = 2m.

1.170n s=nh Analysis 1 (n is the number of strands h is the distance at the free end) Analysis 2 6=3 times h h=2 from s=nh to determine the number of strands, see how many ropes are connected to the movable pulley, there may be one on the axis of the movable pulley, and there must be two on the edge of each movable pulley. There is a maximum of 3 movable pulleys and a maximum of 5 movable pulleys for two movable pulleys.

f＝510/3 n

When calculating the pulling force, you can count the number of strands of rope that are "connected" between movement and stillness, noting that you can't count the strands at the free end, because this strand is not connected. This question is 3

Rose 6 3m

When calculating distances, the numbers are the same.

Answer: Solution: (1) From the question, regardless of the friction and rope weight between the pulley and the shaft, f = (g wheel + g object).

That is: 500N = (G wheel + 900N), the weight of the movable pulley:

g wheel = 100n;

2) The distance that the pull force moves:

s=2h=6m, tensile work:

W total = FS = 500N 6m = 3000J, tensile power power:

p= = =200w；

3) Useful work done by using pulley blocks:

W has = GH = 900N 3m = 2700J, the mechanical efficiency of the pulley block:

Answer: (1) The weight of the movable pulley is 100N;

2) The power of the pulling force is 200W;

2) The mechanical efficiency of the pulley block is 90%.

1. The steering wheel is made bigger and less labor, but the distance of movement will increase.

The thickness of the rope does not have much to do with labor-saving. The main thing is the size of the axis around the rope, which is small and labor-saving, and similarly, the distance of movement will increase.

2。Minimum of 2 pulleys.

First, through a fixed pulley, change the direction of the rope, and then through a movable pulley, the weight is lifted.

It's up-down-up. Of course, the rope has to be tied to the weight at first.