A question of physical mechanical efficiency, in physics, will be called mechanical efficiency

W has = mgh = 200 10 2 = 4000j

W total = mGH + FS = 200 10 2+

Mechanical efficiency = w has w total = 4000 5600 =

Solution: The weight of the object is g=mg=200kg

Because the resistance is a multiple of the weight of the object, the resistance is f=g

The work done by the resistance is the useless work w, which is useless=fs=196n, 8m=1568j, the useful work, the work done to overcome gravity, i.e., w, useful=gh=1960nx2m=3920j

w useful = 200 * 10 * 2 = 4000j

w total = 200*10*

Mechanical efficiency = 1600 4000 = 40 percent.

Gravitational work = mgh = 200 * 10 * 2 = 4000, resistance work =

Mechanical efficiency k=(4000-1600) 4000=60%.

Mechanical efficiency is the ratio of the total work to the total work.

w useful band scramble w total 100% = 80%.

Then the ratio of the useful work of the machinery to the total work is 80%.

In physics, the ratio of useful work to total work is called mechanical efficiency

Therefore, the answer is: the ratio of useful work to total work

1. Fill in the blanks.

1 Extra Work Total Work. 2 useful total extra. 3 Useful Extra Useful Extra 4 60%.

W has =gh=3600n*4m=

w total - w has + w amount =

w has w total = = 60%.

2. Multiple choice questions.

1．d；3．d;

4．d5．b

6 Untitled. 7 B8 D (the first rope has a small number of segments, otherwise it is A) 9 C (five sections of rope to pull up the goods).

10 d Fourth, calculation questions.

1．3000n，125m

One. 1.Extra work.

Total merit 2There is useful work. Total merit.

Extra work. 3.Useful.

Extra. Useful. Extra.

Two.;; The back one is too lazy to do! Apologize. )

1. Fill in the blanks.

1 Extra Work Total Work.

2 useful total extra.

3 Useful Extra Useful Extra.

4 1 44 104j 2 4 104j 60% 2. Multiple choice questions.

1．d2．c

3．d4．d

5．b6．c

7．b8．d

9．c10．d

4. Calculation questions.

1．3000n，125m

2．250n，83．3%

One. 1.Extra work. Total merit.

2.Useful. Total; Extra.

3.Useful Extra Useful Extra.

Solution: (1), because there are 4 sections of rope hanging the movable pulley, so the distance of the free end of the rope is 4 times the height of the object, and the height of the object is 4=4m 4=1m

Useful work: Wu limb patter w has gh=500n*1m=500j2), total work: w total cavity envy = w has =500j 80%=625j3), tensile force:

f=w total s=625j 4m=4), power of tensile work: hungry hole p=w total t=625j 10s=answer: omitted.

If you don't know what you want to ask, remember.

Cargo potential energy change = mgh = 800*.

Note that at this time, it is necessary to overcome the frictional resistance of the plate to do work, so the work is more than the first question) 3Efficiency is equal to the useful work divided by the total work, the useful work refers to the work done directly by moving the object without machinery, that is, 1200J, and the total work refers to the work actually done with the inclined plane, which is 1500J

So the efficiency is 1200 1500 80

1、w=fs=10^4×10m×3=3×10^5 j

2. Fiber p=w t=3 10 5j 50s=6 10 w

3, =w have Huaihu w total = gh fs = g destroy the Ming Tomb 3f =

1) The distance traveled by the tensile force is three times the distance traveled by the object, so w=fs=10 4*30=3*10 55j

2) p=w search clear t=3120 50=

3) W has liquid leakage = gh=

w has w total = 3 * 10 55j =

1. Judging from the topic, the frictional force is ignored at this time, and the work done by the tensile force is transformed into two aspects, one is to do work on the pulley block, and the other is to do work on the object.

The total work done by the tensile force is w=fs=16n*

The work done by the pulling force on the object is to make the object rise.

So the work done on the object w = gh = 40*

Therefore, the work done on the pulley block is w slip = w - w object =

The first question, the work done by the pulling force on the pulley block is the total work w=fs=16n

Work done on an object is useful work, w has = gh = 40n

The second question is that the mechanical efficiency of the pulley block cannot be found because the rope end tension is not known.

Junior high school physics questions, support first-floor answers.

It is not easy to use any machinery.

The control variable method is not used, if the stem of the question has "when the total work is constant", then the question is correct as above, and if the stem has "when the useful work is certain", then the question is correct The sum of the useful work and the extra work is the total work.