Question

Срочно (Физика 7 класс) ПОМОГИТЕ РЕШИТЬ ЗАДАЧКИ 1. Определите архимедову силу действующую на бетонную плиту объемом 20 м3, погруженную в керосин. 2. Какую силу надо приложить, чтобы удержать в воде бетонную плиту объемом 20 м3?

Answer 1

Ответ:

1.Fa=gVp

где V объём тела. p-плотность жидкости

плотность керосина = 800кг на метр в кубе

20 см3=0,00002m3

Fa=10*0,00002m3*800кг на метр в кубе=0,16H

2.

F+Fa=mg F=mg-Fa=mg-p*V*g=g(m-V*p) V=m/p=20/2300=0,3 F=10*(20-0,3*1000)=-280*420=-117600Н

Answer 2

Archimedes' Principle and Buoyant Force

To solve the given problems, we need to understand Archimedes' principle and the concept of buoyant force.

Archimedes' Principle states that when an object is submerged in a fluid (liquid or gas), it experiences an upward force called the buoyant force. The magnitude of the buoyant force is equal to the weight of the fluid displaced by the object.

Now let's solve the given problems step by step.

Problem 1: Archimedes' Force on a Concrete Slab

The first problem asks us to determine the Archimedes' force acting on a concrete slab with a volume of 20 m³ when it is submerged in kerosene.

To find the Archimedes' force, we need to calculate the weight of the kerosene displaced by the concrete slab. The weight of the displaced kerosene is equal to the buoyant force acting on the slab.

To calculate the weight of the kerosene, we can use the formula:

Weight = Density × Volume × Acceleration due to gravity

The density of kerosene can be found in the search results, which is approximately 820 kg/m³ [[1]].

Using this information, we can calculate the weight of the kerosene displaced by the concrete slab:

Weight of kerosene = Density of kerosene × Volume of slab × Acceleration due to gravity

Substituting the given values:

Weight of kerosene = 820 kg/m³ × 20 m³ × 9.8 m/s²

Calculating this expression will give us the weight of the kerosene displaced by the concrete slab, which is equal to the Archimedes' force acting on the slab.

Problem 2: Force Required to Hold the Concrete Slab in Water

The second problem asks us to determine the force required to hold the same concrete slab with a volume of 20 m³ in water.

To solve this problem, we need to find the buoyant force acting on the concrete slab when it is submerged in water. The buoyant force is equal to the weight of the water displaced by the slab.

The density of water can be found in the search results, which is approximately 1000 kg/m³ [[2]].

Using this information, we can calculate the buoyant force acting on the concrete slab:

Buoyant force = Density of water × Volume of slab × Acceleration due to gravity

Substituting the given values:

Buoyant force = 1000 kg/m³ × 20 m³ × 9.8 m/s²

Calculating this expression will give us the buoyant force acting on the concrete slab when it is submerged in water. To hold the slab in water, an equal and opposite force must be applied, which is the force required to hold the slab in water.

I hope this helps! Let me know if you have any further questions.

[[1]] Source: [Density of kerosene](https://www.engineeringtoolbox.com/kerosene-d_980.html) [[2]] Source: [Density of water](https://www.engineeringtoolbox.com/water-density-specific-weight-d_595.html)