Solving a problem using energy and conservative forces concepts

In summary, the conversation discusses a homework problem involving finding the work done by a force P on a ball with constant speed. The diagram is taken from a book that solved the problem using integration, but it can be solved easily using the concept of conservative forces. The potential energy change is equal to the negative of the work done, and in this system, only conservative forces do not change the total energy of the particle. Force P is non-conservative and does change the kinetic energy, which can be seen from the figure. The correct solution involves setting the total work done equal to 0 and using the formula for gravitational potential energy. Thanks to the discussion, it is determined that the solution does not require the use of energy concepts.
  • #1
Hernaner28
263
0

Homework Statement


attachment.php?attachmentid=46109&stc=1&d=1334149747.jpg


It asks me to work out the work done by force P and it tells me that the ball m has a CONSTANT speed during its displacement.

That diagram is taken from a book which has already solved the excercise without using the concepts of energy and conservative forces. It used a complicated way of integrating to determinate the work of P. So since all the forces are conservative this could be solved easily, couldn't it?

Homework Equations


The Attempt at a Solution


If the speed is constatnt then the ΔK is 0. And we know that ΔK=W so W=0. And we also know that the potential energy ΔU=-W so ΔU=0. But after that I end up writing the integral of P when I don't want to do that. Thanks!
 
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  • #2
delta U=-W, are you sure?
 
  • #3
darkxponent said:
delta U=-W, are you sure?

Yes, that's a definition. The change of potential energy is ΔU=-W - what's wrong with it?
 
  • #4
well this applies only when the object is acted apon by conservative forces only. That is delta U +delta K =0.
 
  • #5
Yes I know but are you saying that in this system there's a force which is non-conservative? There's the tension, the weight and force P... oh, force P? hmm...
 
  • #6
You can solve it withput using integral. Just concentrate on work done on the particle by the individual forces
 
  • #7
OK I'll write that down for each force, but is this a conservative system, right? Now you've said that I am in doubt if P is or not conservative.
Thanks
 
  • #8
p os not conservagive force. Work done by p depends on path taken. You can see from the figure. Only those forces are conservative which do not change the total energy of particle. P does changes the kinetic energy of body and hence it is non-conservagive
 
  • #9
Hmmm.. I see. So there's no need to use energy concepts either.

[tex]\begin{array}{l}
{W_T} = 0\\
{W_T} = {W_P} + {W_W} + {W_{tension}}\\
0 = {W_P} - mgh\\
{W_P} = mgh
\end{array}[/tex]

Is this right?

Thanks!
 
  • #10
yes that is correct
 

1. What is the definition of energy in a scientific context?

In physics, energy is defined as the ability to do work or cause change. It can exist in different forms, such as kinetic energy, potential energy, and thermal energy.

2. How are energy and conservative forces related?

Conservative forces are those that do not dissipate energy, meaning that the total amount of energy in a system remains constant. This is known as the principle of conservation of energy. In other words, conservative forces can convert one form of energy into another, but the total amount of energy remains the same.

3. How can energy and conservative forces be used to solve a problem?

When solving a problem using energy and conservative forces concepts, one can use the principle of conservation of energy to analyze the different forms of energy present in a system and how they are transformed or transferred. This can help determine the final state of the system and solve for unknown quantities.

4. Can energy and conservative forces concepts be applied to all types of systems?

Yes, energy and conservative forces concepts can be applied to all types of systems, as long as the principle of conservation of energy holds true. This includes mechanical systems, electrical systems, and even chemical reactions.

5. Are there any limitations to using energy and conservative forces to solve a problem?

While energy and conservative forces concepts are powerful tools in problem-solving, they do have some limitations. For example, they cannot be applied to systems where non-conservative forces, such as friction, are present. Additionally, they may not be applicable to systems with rapidly changing forces or those that involve quantum mechanics.

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