As shown in the figure, a piece of lead is hung under an inflated balloon with a thin thread, put it into the water, and it is just in a static state somewhere. If some water is slowly released from the bottom, the lead and the balloon () A. Still able to stand still B. move down C. move up D. stand still. It's possible to move up or down

As shown in the figure, a piece of lead is hung under an inflated balloon with a thin thread, put it into the water, and it is just in a static state somewhere. If some water is slowly released from the bottom, the lead and the balloon () A. Still able to stand still B. move down C. move up D. stand still. It's possible to move up or down

The balloon and the lead block are in a static state, and the buoyancy of the balloon and the lead block is equal to the gravity of the lead block. Slowly release some water from the bottom, the depth of the upper water decreases, and the pressure of the water also decreases. As the volume of the small balloon increases, the buoyancy of the water on the small balloon increases. At this time, the gravity of the lead block is less than the buoyancy of the balloon and the lead block, so it floats up

When a pulley block composed of a movable pulley and a fixed pulley is used to lift a heavy object, the pulling force of a person on the rope is 70N, and the weight of each pulley is 10N______ The weight of N can be lifted at most______ The weight of n

When there are two sections of rope on the moving pulley, the gravity of the extracted weight is g = 2f-gdynamic = 2 × 70n-10n = 130n. When there are three sections of rope on the moving pulley, the gravity of the extracted weight is GDA = 3f-gdynamic = 3 × 70n-10n = 200N

The lifting weight of pulley block is 220n, and the weight of movable pulley is 20n, regardless of the friction between pulley and shaft and the weight of rope,
N = 3, the power of the pulling force is________ Why isn't. W 16? Isn't it f = g / N

W=（M+m）gH=GH=240x6=1440J
P=W/t=1440/5=288W
It has nothing to do with the number of strands of the rope, because the number of strands of the rope just reflects the tension and the length of the rope. At this time, the tension is f = g / N, the length of the rope is L = NH, and the work is constant

As shown in the figure, a force F of 120N is used to lift the object with weight of G by 2m at a uniform speed, and the weight of the movable pulley is 10N, regardless of the rope weight and friction
1. Distance of pulling force F
2. The work done by pulling force F

1. N (number of rope segments on moving pulley) = 2 h (lifting height of object) = 2 m
S rope (f moving distance) = n * H = 2 * 2m = 4m
A: moved 4 meters
2.F=120N S=4m
W=F*S=120N*4m=480J
A: the work done is 480j

Regardless of friction and rope mass, the fixed pulley, movable pulley and pulley block (two fixed pulleys and two movable pulleys) are used to lift the same object to the same height at a constant speed. Who is more efficient and who is less efficient?

The fixed pulley is the largest, which is 100%. The pulley block is the smallest
Mechanical efficiency η = w / W total = g matter H / Fs
Because f = g total / N, s = NH, so η = g matter / g total
The fixed pulley g total = g object is also used, so η = g object / g total = 100%
Moving pulley g total = g object + G motion, so η = g object / g total = g object / (g object + G motion)
Pulley block g total = g object + 2G movement, so η = g object / g total = g object / (g object + 2G movement)

A worker stands on the ground and uses a fixed pulley and a movable pulley to form a pulley block (excluding friction and rope weight) to increase the 400N goods by 4m at a uniform speed after 10s. The pulling force is 250N
① What is the power of the worker's work?
② What is the mechanical efficiency of the pulley block at this time?
③ How much pulling force does a worker have to use to lift an 800N weight?

① The total work done by workers w = FS = FNH = 250N × 2 × 4m = 2000j
The power of a worker's work
Ptotal = wtotal / T = 2000j / 10s = 200W
② W = GH = 400N × 4m = 1600j
Mechanical efficiency
η = w useful / W total = 1600j / 2000j = 80%
③ When the initial weight is 400N, the pulling force is 250N, according to f = 1 / N × (g object + G wheel)
The gravity of the moving pulley is
G wheel = nf-g object = 2 * 250n-400n = 100N
When G '= 800N, the tensile force
F '= 1 / N × (g object' + G wheel) = 1 / 2 × (800 + 100) n = 450N

A pulley block composed of a moving pulley and a fixed pulley is used to lift a 150n object at a uniform speed of 1m. Regardless of the rope weight and friction, the efficiency of the pulley block is 60%
Find out (1) the size of pulling force and (2) the weight of moving pulley

If there is no picture, I will count it by pulling down the rope. If there is any mistake, please point out:
(1) Active work: Wye = GH = 150n * 1m = 150j
Total work: wtotal = Wye / η = 150 / 60 = 250j
Tension: F = wtotal / S = wtotal / (2H) = 250 / (2 * 1) = 125J
(2) W amount = w total - w you = 250j-150j = 100J
The work done on the moving pulley is extra work,
Gravity of moving pulley: gdynamic = w / h = 100J / 1m = 100N

The pulley block composed of n fixed pulleys and N movable pulleys is used to lift the weight g at a constant speed (excluding the mass and friction of movable pulleys). If the tension applied to the free end of the rope is downward, the tension is (), and if the tension is upward, the tension is ()
Not for answers, just for explanations!

If it is a common assembly method, the pulling force is downward, and a movable pulley is lifted by two sections of rope. The total length of rope bearing the weight is 2n, and the pulling force is one of 2n of the material weight. If the pulling force is upward, a section of rope is added on the hook, and the pulling force is one of (2n + 1) of the material weight

As shown in the figure, regardless of rope weight and friction, when the pulley block lifts objects with a weight of 200N, the mechanical efficiency is 50%? (2) When the weight of the object is 400N, how much tension is needed to make the object rise? If the rising speed of the object is 0.5m/s, what is the power of the pulling force? (3) If the maximum tension of the rope is 800N, what is the mechanical efficiency of the pulley block?

As can be seen from the figure, n = 4, (1) ∵ η = w, total w = G & nbsp; HFS = G & nbsp; hf4h = GF × 4, ∵ f = g, η × 4 = 200n50% × 4 = 100N, ∵ f = 14 (G + G), i.e. 100N = 14 (200N + G), ∵ g = 200N, when the friction and rope weight are not considered, ∵ f = 14 (G + G), i.e. 100N = 14 (200N + G), ∵ g = 200N

Someone lifted the 100N sand to the 6m high building. The bucket weighs 20n and the human body weighs 480n
1. When a person is carrying the sand bucket directly, what is the useful work to be done___ J. What's the bonus___ J. The total contribution is___ J. What is the mechanical efficiency___ ;
If you are upstairs, you need to use 10N pulley___ J. What's the bonus___ J. The total contribution is___ J. What is the mechanical efficiency___ ;
3. If the bucket in 2 is replaced by a 5N heavy bag to hold sand, the lifting process is heavy, and the useful work to be done is as follows___ J. What's the bonus___ J. The total contribution is___ J. What is the mechanical efficiency___ ;
Explain the reason properly!

1. Active work: W1 = GH = 100N * 6m = 600J, extra work: W2 = (g barrel + G person) H = (20n + 480n) * 6m = 3000j, total type: wtotal = W1 + W2 = 600J + 3000j = 3600j, mechanical efficiency: η = W1 / wtotal = 600J / 3600j = 16.7%. 2. Active work: for example, 1 is 600J, extra work: W3 = g pulley * H = 10N * 6m = 60j, total work: wtotal 2 = W1 + W3 = 660j