Physics Forums (http://www.physicsforums.com/index.php)
-   Classical Physics (http://www.physicsforums.com/forumdisplay.php?f=61)
-   -   Work done by a spring & its potential energy (http://www.physicsforums.com/showthread.php?t=652153)

 Archit Patke Nov14-12 07:50 AM

Work done by a spring & its potential energy

According to work - mechanical energy theorem ,
W = K(final) - K(initial) + U(final) - U(initial) . . . . (1)
as we define Potential energy as negative of work done by conservative force and assuming that the only force in this situation is Spring force then ,
W(spring) = K(final) - K(initial)
As work done is calculated by finding component of spring force in direction of displacement. How can we say that U(final) - U(initial) applies for all possible conditions of extension of spring as displacement may not be in direction of force ?
Spring force = 0.5kx2

 Andrew Mason Nov14-12 09:17 AM

Re: Work done by a spring & its potential energy

Quote:
 Quote by Archit Patke (Post 4158803) According to work - mechanical energy theorem , W = K(final) - K(initial) + U(final) - U(initial) . . . . (1) as we define Potential energy as negative of work done by conservative force and assuming that the only force in this situation is Spring force then , W(spring) = K(final) - K(initial) As work done is calculated by finding component of spring force in direction of displacement. How can we say that U(final) - U(initial) applies for all possible conditions of extension of spring as displacement may not be in direction of force ? Spring force = 0.5kx2
Welcome to PF!

First of all, your equation (1) defines the external work done by/on a system. If no energy is added or lost (Wext = 0), Kf + Uf = Ki + Ui.

Second, your question is not clear. What do you mean when you say U(final) - U(initial) applies? U(final) - U(initial) is not a mathematical statement.

Finally, your statement: Spring force = 0.5kx2 is not correct. F = -kx.

AM

 Studiot Nov14-12 03:23 PM

Re: Work done by a spring & its potential energy

Quote:
 Finally, your statement: Spring force = 0.5kx2 is not correct. F = -kx.
In case this was a simple slip, the formula

$$W = \frac{1}{2}k{e^2}$$

W = work, e = extension, k = spring constant

Refers to the work done in extending a spring = potential energy stored in that spring on extension.

 All times are GMT -5. The time now is 04:34 AM.