Nonlinear spring energy problem

In summary, the conversation is about finding the change in potential energy U when a nonlinear spring is stretched by 2m from its equilibrium position. The formula for the force F required to stretch the spring is given as F=40x-6x^2 and the formula for potential energy is U=.5kx^2. The initial attempt at solving for U results in 56J, but after recognizing that F is not equal to kx, the correct solution is found by integrating F=-dU/dx, which gives U=-64J. Therefore, the change in potential energy and work done is 64J.
  • #1
lzh
111
0

Homework Statement


The stretch of a nonlinear spring by an amount x requires a force F given by:
F=40x-6x^2
where F is in Newtons and x is in meters.

What is the change in potential energy U when the spring is stretched 2m from its equilibrium position?


Homework Equations


U=.5kx^2
= .5(kx)x
F=kx

The Attempt at a Solution


F=40(2)-6(2)^2=80-24=56N
U=.5(56N)(2)=56J

Thats what I thought would work, but 56J is no the correct answer. What am I doing wrong?
 
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  • #2
F=-dU/dx

use this
 
  • #3
So it'd be:
56N(2m)=-dU
dU=-112?
Am I not getting this?
 
  • #4
lzh said:

Homework Statement


The stretch of a nonlinear spring by an amount x requires a force F given by:
F=40x-6x^2
where F is in Newtons and x is in meters.

What is the change in potential energy U when the spring is stretched 2m from its equilibrium position?


Homework Equations


U=.5kx^2
= .5(kx)x
F=kx

The Attempt at a Solution


F=40(2)-6(2)^2=80-24=56N
U=.5(56N)(2)=56J

Thats what I thought would work, but 56J is no the correct answer. What am I doing wrong?
The trick here is to recognize that F=40x-6x^2 which is not the same as F=kx.

Now U(x) = [tex]\int^x_0\,F(x) dx\,=\,\int^x_0\,kx\,dx[/tex]

http://hyperphysics.phy-astr.gsu.edu/hbase/pespr.html#pe2

http://hyperphysics.phy-astr.gsu.edu/hbase/pegrav.html#pe
 
  • #5
Oh, I see!

Thanks, I got it!
 
  • #6
f=-dU/dx
integrating both sides
20x^2 -2x^3=-U
put x=2
U=-64J

change would be 64...and work done would be 64 J
 

Related to Nonlinear spring energy problem

1. What is a nonlinear spring energy problem?

A nonlinear spring energy problem is a mathematical and physical problem that involves the behavior of a spring that does not follow Hooke's Law, which states that the force exerted by a spring is directly proportional to its displacement. Nonlinear springs do not follow this relationship and can be more complex to analyze.

2. What factors affect the behavior of a nonlinear spring?

The behavior of a nonlinear spring is affected by several factors, including the material properties of the spring, the shape and size of the spring, the amount of force applied, and the initial position of the spring. These factors can all impact the energy stored in the spring and its response to external forces.

3. How is the energy stored in a nonlinear spring different from a linear spring?

The energy stored in a nonlinear spring is different from a linear spring because it does not follow Hooke's Law. In a linear spring, the energy stored is directly proportional to the displacement of the spring, while in a nonlinear spring, this relationship is more complex and can vary based on the factors mentioned above.

4. How can the energy stored in a nonlinear spring be calculated?

The energy stored in a nonlinear spring can be calculated using mathematical equations that take into account the material properties of the spring, the amount of force applied, and the displacement of the spring. These equations can be derived from the potential energy of the spring and its corresponding force-displacement curve.

5. What are some real-world applications of nonlinear spring energy problems?

Nonlinear spring energy problems have many real-world applications, including in mechanical and structural engineering, where they can be used to design and analyze complex systems such as suspension bridges and car suspensions. They are also used in the development of new materials and in the study of natural phenomena such as earthquakes and ocean waves.

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