# Krotov problem: how to write Energy conservation for this fluid?

• ermia
In summary, The conversation discusses the use of a potential equation involving fluid parts and the relevance of calculating the radius in relation to the cross sectional area. The equation for the radius is incorrect and there is a discussion about the relevance of calculating it.
ermia
Homework Statement
I uploaded the problem. when I want to write the potential energy of the fluid in the initial and final state I don't find the right answer. I know the rest of the problem.
Relevant Equations
$$U=\rho g h A h_{cm}$$
I wrote some potentials but they were wrong. I used the cm of all fluid parts and I used the radius which is $$\sqrt S/ \pi$$ .

#### Attachments

• Apt.jpg
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That equation for radius has a "type" error.
$$r =\sqrt \frac{S}{\pi}$$

Per forum rules, please post your working. Otherwise we have no way to know where you are going wrong.

Could you explain how is that radius, which is not shown as data in the problem, relevant?

Lnewqban said:
Could you explain how is that radius, which is not shown as data in the problem, relevant?
S is the cross sectional area, so ##S=\pi r^2##. But if you are asking why bother calculating the radius (you don't even have to assume it is a circular cross section) then I agree.

ChiralSuperfields and Lnewqban

## 1. What is the Krotov problem?

The Krotov problem is a mathematical optimization problem that involves finding the optimal control of a dynamical system in order to achieve a desired final state. It is often used in the field of optimal control theory and has applications in various areas such as physics, engineering, and economics.

## 2. How is energy conservation related to the Krotov problem?

Energy conservation is an important aspect of the Krotov problem because it ensures that the optimal control solution is physically feasible. In other words, the control inputs should not violate the laws of physics and result in an energy-conserving trajectory for the system.

## 3. What is the significance of writing energy conservation for the fluid in the Krotov problem?

In the Krotov problem, the fluid is often used as the dynamical system that needs to be controlled. Writing energy conservation for the fluid ensures that the control inputs do not result in any energy losses or gains in the system, which can affect the final state and the optimality of the solution.

## 4. How can energy conservation be written for the fluid in the Krotov problem?

Energy conservation for a fluid in the Krotov problem can be written using the Euler-Lagrange equations, which are a set of differential equations that describe the dynamics of the system. These equations take into account the energy of the fluid and its interaction with the control inputs to ensure that energy is conserved throughout the system's trajectory.

## 5. What are the challenges of writing energy conservation for the fluid in the Krotov problem?

One of the main challenges of writing energy conservation for the fluid in the Krotov problem is the complexity of the equations involved. The Euler-Lagrange equations can be difficult to solve analytically, and numerical methods are often used to find approximate solutions. Additionally, the specific properties and behavior of the fluid must be taken into account, which can vary depending on the application and system being studied.

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