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JenniferSmart1
 3 years ago
Why is kx=25N instead of kx=25N?
JenniferSmart1
 3 years ago
Why is kx=25N instead of kx=25N?

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JenniferSmart1
 3 years ago
Best ResponseYou've already chosen the best response.1shouldn't F=kx?

Outkast3r09
 3 years ago
Best ResponseYou've already chosen the best response.1Ahh this my physics teacher went over

JenniferSmart1
 3 years ago
Best ResponseYou've already chosen the best response.1cool! Now you can explain it to me :)

Outkast3r09
 3 years ago
Best ResponseYou've already chosen the best response.1the negative explains how that force is acting upon the spring

Outkast3r09
 3 years ago
Best ResponseYou've already chosen the best response.1it depends on the what you're trying to find

Outkast3r09
 3 years ago
Best ResponseYou've already chosen the best response.1if you're trying to find the force the spring is exerting on the mass or the mass exerting on the spring

JenniferSmart1
 3 years ago
Best ResponseYou've already chosen the best response.1Hmmm let's seedw:1353379482698:dw

Outkast3r09
 3 years ago
Best ResponseYou've already chosen the best response.1dw:1353379572781:dw

JenniferSmart1
 3 years ago
Best ResponseYou've already chosen the best response.1well I guess we're stretching to a certain length, so the first figure?

JenniferSmart1
 3 years ago
Best ResponseYou've already chosen the best response.1I mean the first figure you drew

Outkast3r09
 3 years ago
Best ResponseYou've already chosen the best response.1the figures are the same

Outkast3r09
 3 years ago
Best ResponseYou've already chosen the best response.1it depends on whether you're trying to find the length of the spring or the position of the mass

JenniferSmart1
 3 years ago
Best ResponseYou've already chosen the best response.1Uhm 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

Outkast3r09
 3 years ago
Best ResponseYou've already chosen the best response.1if it asked abouthe spring itself it'd be negative

Outkast3r09
 3 years ago
Best ResponseYou've already chosen the best response.1there 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

Outkast3r09
 3 years ago
Best ResponseYou've already chosen the best response.1so since it's asking for position of the mass it's thisdw:1353379915405:dw

JenniferSmart1
 3 years ago
Best ResponseYou've already chosen the best response.1why is it positive? because it is going in the direction that we designated as positive?

Outkast3r09
 3 years ago
Best ResponseYou've already chosen the best response.1technically this question can have 2 answers + answer and a  answer depending on how you set up your axis

JenniferSmart1
 3 years ago
Best ResponseYou've already chosen the best response.1OH I see! dw:1353380068540:dw Like so?

JenniferSmart1
 3 years ago
Best ResponseYou've already chosen the best response.1Now I can say that F=kx

JenniferSmart1
 3 years ago
Best ResponseYou've already chosen the best response.1no the other way around, I should probably make the restoring force positive...

Outkast3r09
 3 years ago
Best ResponseYou've already chosen the best response.1dw:1353380229463:dw

Outkast3r09
 3 years ago
Best ResponseYou've already chosen the best response.1yeah the picture they used was probably a free falling mass

Outkast3r09
 3 years ago
Best ResponseYou've already chosen the best response.1and saying that the sum of the force of gravity + any other force = F

JenniferSmart1
 3 years ago
Best ResponseYou've already chosen the best response.1Yeah that makes more sense. so they probably had up as positive and down as negative.

Outkast3r09
 3 years ago
Best ResponseYou've already chosen the best response.1yes 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

JenniferSmart1
 3 years ago
Best ResponseYou've already chosen the best response.1so why is k(0.2) why 0.2? How did they come up with x=0.2?

JenniferSmart1
 3 years ago
Best ResponseYou've already chosen the best response.1that's the displacement haha

Outkast3r09
 3 years ago
Best ResponseYou've already chosen the best response.1yes the displacement will still be posive

JenniferSmart1
 3 years ago
Best ResponseYou've already chosen the best response.1hmm 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....

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

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

JenniferSmart1
 3 years ago
Best ResponseYou've already chosen the best response.1potential energy as positive...the restorative force?

JenniferSmart1
 3 years ago
Best ResponseYou've already chosen the best response.1Yes that makes sense

JenniferSmart1
 3 years ago
Best ResponseYou've already chosen the best response.1I had to reread the last sentence you wrote several times, but it makes sense now

JenniferSmart1
 3 years ago
Best ResponseYou've already chosen the best response.1but where did they get the 8 in sin and cos 8t

CliffSedge
 3 years ago
Best ResponseYou've already chosen the best response.0As 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.

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

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

JenniferSmart1
 3 years ago
Best ResponseYou've already chosen the best response.1yep, sounds good. I googled it LOL \[T=2\pi \sqrt{\frac mk}\]

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

JenniferSmart1
 3 years ago
Best ResponseYou've already chosen the best response.1so the formula is \[x(t)=c_1cosTt+c_2sinTt\]

JenniferSmart1
 3 years ago
Best ResponseYou've already chosen the best response.1so T is \[\omega\]

CliffSedge
 3 years ago
Best ResponseYou've already chosen the best response.0\(\large . . . cos(\omega t) . . \) No, ω is related to T.

JenniferSmart1
 3 years ago
Best ResponseYou've already chosen the best response.1Oh \[\omega=\sqrt{\frac km}\]

JenniferSmart1
 3 years ago
Best ResponseYou've already chosen the best response.1\[x(t)=c_1cos\omega t+c_2sin\omega t\]

CliffSedge
 3 years ago
Best ResponseYou've already chosen the best response.0Yes, 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 ;) )

JenniferSmart1
 3 years ago
Best ResponseYou've already chosen the best response.1leaning more towards engineering....physics formula sheet :P

JenniferSmart1
 3 years ago
Best ResponseYou've already chosen the best response.1omega doesn't seem to have units

CliffSedge
 3 years ago
Best ResponseYou've already chosen the best response.0That 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..)

CliffSedge
 3 years ago
Best ResponseYou've already chosen the best response.0omega should have units of s^1, it's a frequency.

CliffSedge
 3 years ago
Best ResponseYou've already chosen the best response.0Or .. 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.

JenniferSmart1
 3 years ago
Best ResponseYou've already chosen the best response.1radians per second

JenniferSmart1
 3 years ago
Best ResponseYou've already chosen the best response.1according to my friend wiki

JenniferSmart1
 3 years ago
Best ResponseYou've already chosen the best response.1so s^1 should be sufficient, i can leave the radians part out in my notation?

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

JenniferSmart1
 3 years ago
Best ResponseYou've already chosen the best response.1why 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

JenniferSmart1
 3 years ago
Best ResponseYou've already chosen the best response.1Thanks everyone!!!!
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