Weld circles with 7-meter-long steel bars, each of which has a diameter of 2 decimeters. How many such circles can this steel bar weld? (excluding Street)

Up to 11, 7 meters = 70 decimeters, pie = 3.14, 3.14 times 2 = 6.28 (the area of a circle), 70 is more than 6.28 = 11, so it is 11

The largest cuboid frame is welded with 64 decimeter long steel bars. The length is 1 / 2 more than the width``````
Use 64 decimeter long steel bar to weld the largest cuboid frame. The length is 1 / 2 more than the width, and the height is 1 / 2 less than the width. How should this steel bar be cut?
I want to help you today

Let the width be X
The length is x + X / 2 = 3x / 2 and the height is x-1.5
(X+3X/2+X-1.5)*4=64
The solution is x = 5, that is, the width is 5
The length is 7.5 and the height is 3.5

How many decimeters of steel bar is needed to weld a rectangular frame with 8dm long, 5DM wide and 6dm high?

（8+5+6）x4
=19x4
=76（dm）

When the density of an object immersed in a liquid is greater than that of the liquid, is it buoyant

The object is buoyant, but f floats < g, and the object sinks

(Kunming, 2011) when exploring the "factors affecting the buoyancy", a class guessed that the buoyancy might be related to the density of the liquid, the depth of the object immersed in the liquid, and the volume of the object expelling the liquid. The teacher prepared the following experimental equipment for the students: ① spring dynamometer, ② glass beaker with water, ③ glass beaker with alcohol, and ④ hook on the top Aluminum block, thin wire
(1) To explore whether the buoyancy is related to the depth of the object immersed in the liquid, the equipment to be selected is the aluminum block with hook on the top, thin wire And (fill in the serial number) (2) student a thinks that "the deeper the object is immersed in the liquid, the greater the buoyancy it receives", and in the same kind of liquid, he uses the experiment of figure a to confirm his point, that is, the buoyancy of the aluminum block increases from a to a '. Student B thinks that "the buoyancy has nothing to do with the depth of the object immersed in the liquid", and uses the experiment of figure B to confirm his point of view in the same kind of liquid Point, that is, the buoyancy of the aluminum block does not change from B to B '. Please analyze the experimental process of students a and B. what do you think is incorrect The reason is (3) after careful analysis, it is found that the experiment of student a is suitable for exploring the size and size of buoyancy__ Relationship

(1) To explore the relationship between the buoyancy and the depth of the object immersed in the liquid, it is necessary to ensure that the density of the liquid and the volume of the liquid arranged by the object are fixed. However, the depth of the object immersed in the liquid is different. The buoyancy needs to be measured by a spring dynamometer and some liquid

The buoyancy problem of physics in the third year of junior high school: the equal volume hydrogen balloon and air balloon are both in the air, which one has the greatest buoyancy? In the water

Buoyancy is the same. Because buoyancy = the density of liquid or gas * g * the volume of liquid or gas. In air or in water, the volume of air or water is equal, but the density of air or water is constant, so buoyancy is the same. The hydrogen balloon will float up in air and empty balloon will sink because of their different gravity

The volume of a hydrogen balloon is 620 cubic meters. If the air pressure is standard atmospheric pressure, the buoyancy of the balloon near the ground is 7998 n
The volume of a hydrogen balloon is 620 cubic meters. If the air pressure is standard atmospheric pressure, the buoyancy of the balloon near the ground is 7998 n. how many people with a weight of 50 kg can the hydrogen balloon carry when it can be lifted up?

The hydrogen density is 0.09kg/m3,
Hydrogen weight g = 620 * 0.09 * 9.8 = 546.84n,
Buoyancy p-hydrogen weight g = 7451n,
Weight per person = 50 * 9.8 = 490N,
46 / 490 ≈ 15 (person). The maximum weight is 50 kg

What is the relationship between the buoyancy of the same volume hydrogen balloon and air balloon before release?

Equal buoyancy
Archimedes' law applies not only to liquids, but also to uniform gases. Before letting go, the volume of the air they expel is equal, so the gravity and buoyancy of the air they expel are equal

The relationship between the buoyancy of a hydrogen balloon and an air balloon of the same volume before release is: when the balloon is released, it floats up, but the air balloon can not. This is because the buoyancy of the hydrogen balloon (greater than, less than or equal to) the gravity it bears, and the buoyancy of the air balloon (greater than, less than or equal to) the gravity it bears
The first two questions I know. It should be equal buoyancy, buoyancy is greater than gravity
But the last empty answer is that buoyancy is less than gravity, but isn't the density of an empty balloon the same as that of air? It should float. Why isn't it equal to

In addition, the air in the sphere is compressed, and the air density is slightly different from that in the outer space of the balloon. These factors will make the buoyancy of the air balloon lower than that of the gravity and cause the balloon to sink

In festivals, hydrogen balloons are often used to decorate the atmosphere. If the volume of hydrogen balloon is 10m3, the buoyancy in the air is 10% N. If the hydrogen balloon is hung heavily, it can not be made at most When the hydrogen balloon is still in the air, the resultant force is applied__ N. (air density is 1.29 kg / m3, hydrogen density is 0.09 kg / m3, g = 10N / kg)

(1) According to Archimedes' principle: F floating = ρ gas GV row = 1.29kg/m3 × 10N / kg × 10m3 = 129n; (2) cargo: G material = f floating - G ball = f floating - ρ hydrogen GV row = 129n-0.09kg/m3 × 10N / kg × 10m3 = 120N; when resting in the air, it is affected by the balance force, so the resultant force is 0

Weld circles with 7-meter-long steel bars, each of which has a diameter of 2 decimeters. How many such circles can this steel bar weld? (excluding Street)