Question

It took 1700 J of work to stretch a spring from its natural length of 2m to a length of 5m. Find the spring's force constant.

Answer 1

You're looking for "x"?

Answer 2

Well constant is K.. I'm just confused by this whole chapter so far.

Answer 3

I know it uses Hooke's Law, which is F = K * X

Answer 4

X is 5-2.
Use the Work to find the F (there a formula? I forgot)
You're looking for "K" I guess. Ignore the already given constant.

Answer 5

1700 = K - 3?

Answer 6

I mean K * 3

Answer 7

I don't think so. Force is not work. And yes, 3k works for the right side.

Answer 8

Work equals "Force times distance" right?
W=f*d.

Answer 9

So, I guess "d" is probably your "x". Sub in 1700 for W.

Answer 10

F = -kx
1700/3 = -k(5-2)
1700/9 = -k
k = -1700/9

Answer 11

1700=3F

Answer 12

@ Chris: 1700J isn't force...Is it?

Answer 13

Yup. Rearrange 1700=3f so that 1700/3=f. There's your force.

Answer 14

W = Fs
1700 = F(3)
F = 1700/3

Answer 15

None of those have worked for answers.. :/

Answer 16

what are you trying to find

Answer 17

Well that's only a part of it...

Answer 18

He's looking for "K".

Answer 19

But you basically have your "f" and "X". You already tried it with f as 566.666... and x as 3?

Answer 20

yeah I tried +/ 1700/9 and 1700/3

Answer 21

try this
\[F = \Delta K\]
1700 = (1/2)k(3)^2 - 0
(2*1700)/(9) = k

Answer 22

Did you get 188.9?

Answer 23

@Chris, that was correct!

Answer 24

:D

Answer 25

so how did you get that equation?

Answer 26

Aww. I fail at physics.

Answer 27

Yeah this is calculus 2, but for engineers.. Even though I'm a computer science major.

Answer 28

F = -kx <===== this is for when x's natural position is at 0
You have to integrate it if the natural position is elsewhere
\[\int\limits_{0}^{x} F dx = \int\limits_{0}^{x}kx dx = (1/2) kx^2 |0 \to x = (1/2)kx^2 - 0\]