What is the speed of the chain at this instant?

[fball558]

Homework Statement

A chain of metal links with total mass M = 6 kg is coiled up in a tight ball on a low-friction table. You pull on a link at one end of the chain with a constant force F = 69 N. Eventually the chain straightens out to its full length L = 1.0 m, and you keep pulling until you have pulled your end of the chain a total distance d = 3.6 m.

before this question i have already answered these questions. might need the info to solve not sure though.

(a) Consider the point particle system:
What is the speed of the chain at this instant?
8.4439 m/s


Consider the real system:
What is the change in energy of the chain?
delta(E) = 248.4 joules

The Attempt at a Solution

i solved conservation of energy like
Ef = Ei + W + Q
then
Ef = 248.4 + Q where Q = 0
then
final Ke + Ethermal = 248.4
solved for Ethermal = 248.4 / Ke or 248.4/(1/2mv^2) using v found above
i get 1.1613 J but that is wrong. where did i mess up??

 

[sriceb01]

solved for Ethermal = 248.4 / Ke or 248.4/(1/2mv^2) using v found above
i get 1.1613 J but that is wrong. where did i mess up??

Instead of dividing by Ke...You have to subtract by Ke.

 

[fball558]

haha i need to go back to basic math.
thanks sriceb01
and welcome to the forums.
this site is great!