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JenniferSmart1Best ResponseYou've already chosen the best response.1
shouldn't F=kx?
 one year ago

Outkast3r09Best ResponseYou've already chosen the best response.1
Ahh this my physics teacher went over
 one year ago

JenniferSmart1Best ResponseYou've already chosen the best response.1
cool! Now you can explain it to me :)
 one year ago

Outkast3r09Best ResponseYou've already chosen the best response.1
the negative explains how that force is acting upon the spring
 one year ago

Outkast3r09Best ResponseYou've already chosen the best response.1
it depends on the what you're trying to find
 one year ago

Outkast3r09Best ResponseYou've already chosen the best response.1
if you're trying to find the force the spring is exerting on the mass or the mass exerting on the spring
 one year ago

JenniferSmart1Best ResponseYou've already chosen the best response.1
Hmmm let's seedw:1353379482698:dw
 one year ago

Outkast3r09Best ResponseYou've already chosen the best response.1
dw:1353379572781:dw
 one year ago

JenniferSmart1Best ResponseYou've already chosen the best response.1
well I guess we're stretching to a certain length, so the first figure?
 one year ago

JenniferSmart1Best ResponseYou've already chosen the best response.1
I mean the first figure you drew
 one year ago

Outkast3r09Best ResponseYou've already chosen the best response.1
the figures are the same
 one year ago

Outkast3r09Best ResponseYou've already chosen the best response.1
it depends on whether you're trying to find the length of the spring or the position of the mass
 one year ago

JenniferSmart1Best ResponseYou've already chosen the best response.1
Uhm I think we want my figure because In your figure we have to consider the gravitational force and the restoring force. I don't think they want to consider the gravitational force
 one year ago

Outkast3r09Best ResponseYou've already chosen the best response.1
if it asked abouthe spring itself it'd be negative
 one year ago

Outkast3r09Best ResponseYou've already chosen the best response.1
there is two ways this question can be answered 1) How long did the spring stretch from initial 2) What is the position of the mass after initial. They're the same thing
 one year ago

Outkast3r09Best ResponseYou've already chosen the best response.1
so since it's asking for position of the mass it's thisdw:1353379915405:dw
 one year ago

JenniferSmart1Best ResponseYou've already chosen the best response.1
why is it positive? because it is going in the direction that we designated as positive?
 one year ago

Outkast3r09Best ResponseYou've already chosen the best response.1
technically this question can have 2 answers + answer and a  answer depending on how you set up your axis
 one year ago

JenniferSmart1Best ResponseYou've already chosen the best response.1
OH I see! dw:1353380068540:dw Like so?
 one year ago

JenniferSmart1Best ResponseYou've already chosen the best response.1
Now I can say that F=kx
 one year ago

JenniferSmart1Best ResponseYou've already chosen the best response.1
no the other way around, I should probably make the restoring force positive...
 one year ago

Outkast3r09Best ResponseYou've already chosen the best response.1
dw:1353380229463:dw
 one year ago

Outkast3r09Best ResponseYou've already chosen the best response.1
yeah the picture they used was probably a free falling mass
 one year ago

Outkast3r09Best ResponseYou've already chosen the best response.1
and saying that the sum of the force of gravity + any other force = F
 one year ago

JenniferSmart1Best ResponseYou've already chosen the best response.1
Yeah that makes more sense. so they probably had up as positive and down as negative.
 one year ago

Outkast3r09Best ResponseYou've already chosen the best response.1
yes but it really just depends on what you define it... if your teacher marks you wrong and your diagram says otherwise just clear it up with him
 one year ago

JenniferSmart1Best ResponseYou've already chosen the best response.1
so why is k(0.2) why 0.2? How did they come up with x=0.2?
 one year ago

JenniferSmart1Best ResponseYou've already chosen the best response.1
that's the displacement haha
 one year ago

Outkast3r09Best ResponseYou've already chosen the best response.1
yes the displacement will still be posive
 one year ago

JenniferSmart1Best ResponseYou've already chosen the best response.1
hmm interesting: (this the DE part of my calc II book) \[2\frac{d^2x}{dt^2}+128x=0 \text{ has the solution }x(t)=c_1cos8t+c_2sin8t \] yeah that's easier that doing it manually....
 one year ago

CliffSedgeBest ResponseYou've already chosen the best response.0
It's convention to designate potential energy as negative. The reaction force of the spring is opposite the positive applied force.
 one year ago

CliffSedgeBest ResponseYou've already chosen the best response.0
More clearly: The negative sign of F=kx means that the spring force is opposite to the applied force on the spring.
 one year ago

JenniferSmart1Best ResponseYou've already chosen the best response.1
potential energy as positive...the restorative force?
 one year ago

JenniferSmart1Best ResponseYou've already chosen the best response.1
Yes that makes sense
 one year ago

JenniferSmart1Best ResponseYou've already chosen the best response.1
I had to reread the last sentence you wrote several times, but it makes sense now
 one year ago

JenniferSmart1Best ResponseYou've already chosen the best response.1
but where did they get the 8 in sin and cos 8t
 one year ago

CliffSedgeBest ResponseYou've already chosen the best response.0
As others mentioned above, it's a sign convention. You define what direction you want to be positive and anything opposite to that is negative. The norm, though is to treat spring force as negative/opposite to any force acting *on* the spring.
 one year ago

CliffSedgeBest ResponseYou've already chosen the best response.0
The 8 is based on the period of the spring  that is determined by the spring constant, k, and the attached mass.
 one year ago

CliffSedgeBest ResponseYou've already chosen the best response.0
\(\large T=2\pi \sqrt{\frac{m}{k}}\) T^1 is the frequency of oscillation.
 one year ago

JenniferSmart1Best ResponseYou've already chosen the best response.1
yep, sounds good. I googled it LOL \[T=2\pi \sqrt{\frac mk}\]
 one year ago

CliffSedgeBest ResponseYou've already chosen the best response.0
The "8" in the cosine function usually goes by the name, omega, \(\large \omega\). Might want to look that up too.
 one year ago

JenniferSmart1Best ResponseYou've already chosen the best response.1
so the formula is \[x(t)=c_1cosTt+c_2sinTt\]
 one year ago

JenniferSmart1Best ResponseYou've already chosen the best response.1
so T is \[\omega\]
 one year ago

CliffSedgeBest ResponseYou've already chosen the best response.0
\(\large . . . cos(\omega t) . . \) No, ω is related to T.
 one year ago

JenniferSmart1Best ResponseYou've already chosen the best response.1
Oh \[\omega=\sqrt{\frac km}\]
 one year ago

JenniferSmart1Best ResponseYou've already chosen the best response.1
\[x(t)=c_1cos\omega t+c_2sin\omega t\]
 one year ago

CliffSedgeBest ResponseYou've already chosen the best response.0
Yes, you can either derive that using the Diff.Eq. or look it up on a physics formula sheet. (Depends on if you are more mathematician or engineer ;) )
 one year ago

JenniferSmart1Best ResponseYou've already chosen the best response.1
leaning more towards engineering....physics formula sheet :P
 one year ago

JenniferSmart1Best ResponseYou've already chosen the best response.1
omega doesn't seem to have units
 one year ago

CliffSedgeBest ResponseYou've already chosen the best response.0
That would be my choice too, but know that the way the physicists got those formulas in the first place was to solve the DEs (or rather to get their math dept. grad students and TAs to do the solving for them..)
 one year ago

CliffSedgeBest ResponseYou've already chosen the best response.0
omega should have units of s^1, it's a frequency.
 one year ago

CliffSedgeBest ResponseYou've already chosen the best response.0
Or .. is at least based on a frequency, something in the derivation might make the units cancel, but I'm pretty sure it's just the reciprocal of the time period, T.
 one year ago

JenniferSmart1Best ResponseYou've already chosen the best response.1
radians per second
 one year ago

JenniferSmart1Best ResponseYou've already chosen the best response.1
according to my friend wiki
 one year ago

JenniferSmart1Best ResponseYou've already chosen the best response.1
so s^1 should be sufficient, i can leave the radians part out in my notation?
 one year ago

CliffSedgeBest ResponseYou've already chosen the best response.0
Yes, because radians are dimensionless (it's derived from length ÷ length), that's what the 2π conversion factor is in there for.
 one year ago

JenniferSmart1Best ResponseYou've already chosen the best response.1
why is c_2 zero? shouldn't it be ...so when we say\[ x(0)=8c_2 cos8t\] does that mean \[0=8c_2 cos8t=8c_2cos(0)=8c_2(1)=c_2\] yep that seems right LOL
 one year ago

JenniferSmart1Best ResponseYou've already chosen the best response.1
Thanks everyone!!!!
 one year ago
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