Nonconservative work while swimming

[flemj]

Homework Statement

Starting at rest at the edge of a swimming pool, a 67.0 athlete swims along the surface of the water and reaches a speed of 1.15 by doing the work = 171 . Find the nonconservative work, , done by the water on the athlete.

Homework Equations

(m)(a)(x initial) + .5 (m)(v^2 initial) = (m)(a)(x final) + .5 (m)(v^2 final)
E=UK
W=Fd
F=ma
K=.5 mv^2

The Attempt at a Solution

Im not really sure how to tackle this problem those are the equations i think i need to use but should it go something like

K=.5(67kg)(1.15m/s^2) so K=44.3
E=UK (U being the work?) E= (171)(44.3) E=7575.3

i don't know what I am doing i need some help that'd be great

 

[physics girl phd]

E=UK

You have an error in your equation: E=UK. It would normally be: E = U + K

The equation is meant to demonstration conservation of energy: Energy equals potential energy plus kinetic. U is typically potential energy, which is usually a conservative form of energy because potential is gravitational or electrical potential energy... or maybe elastic potential too (in frictionless springs).

What you really want is something called the "work-energy theorem"... and even better form of conservation of energy, because now you could put work in (ex. chemical reactions like those in your own body converting chemical energy, or energy in the form of electrical bond in chemicals, to usable forms) or take work out (ex. lost of energy to heat (kinetic energy in microscopic particles like molecules or atoms).. look up that.

 

[flemj]

sorry i wrote that down wrong but your saying i want to use W=Delta Ek ? how do i go about that tho? by using K=.5 mv^2?

 

[physics girl phd]

sorry i wrote that down wrong but your saying i want to use W=Delta Ek ? how do i go about that tho? by using K=.5 mv^2?

Think again about the physics... NOT just equations!
You're swimming. You use some chemical energy to do that: how much?

Then: what do you get out of it?

Then: As the problem asks for: Did you get everything out of it that you could have if the situation worked perfect for you? If not: what did you lose in the process?

 

[flemj]

Think again about the physics... NOT just equations!
You're swimming. You use some chemical energy to do that: how much?

Then: what do you get out of it?

Then: As the problem asks for: Did you get everything out of it that you could have if the situation worked perfect for you? If not: what did you lose in the process?

yes so while swimming my conservative energy would be 77.05 and in a nonconservative force I am losing some of that energy due to the friction and the heat that I am giving off etc. to solve for this equation do i need to find the distance i have swam ? i understand why it happened just now how to calculate the lose