Valhalla Legends Archive

I just bombed my physics test yesterday. It was about Work, and Power, and all that other shit...

Anyone familiar with that shit lol...
Another bad start in this semester.. Blah

Quote from: Chopz on February 10, 2004, 10:01 PM
I just bombed my physics test yesterday. It was about Work, and Power, and all that other shit...

Anyone familiar with that shit lol...
Another bad start in this semester.. Blah

Funny, I just dominated my Physics (1110) midterm.  Although this is probably not the right place to post this, since you're not discussing mathemetics per se...

Quote from: Chopz on February 10, 2004, 10:01 PM
Anyone familiar with that shit lol...

Yes.

Quote from: K on February 10, 2004, 10:22 PM
Although this is probably not the right place to post this, since you're not discussing mathemetics per se...

No, it's fine under forum rule 3.4.

Well, if it was just work/power then all you have to know are the basic principles of what work really is, and then how power relates to work...
Did you also have to deal with conservation of energy and such?
Also, being able to manipulate the equations is kind of important...
Work = Force * Distance but also the change in Kinetic Energy... so W = delta KE where KE = 1/2 mass * velocity^2
If you can, provide a specific question you had a problem with, so I can see how they are testing you.

Yes, do provide some questions you are having trouble with. Physics is fun!

Quote from: cipher on February 11, 2004, 04:48 PM
Well, if it was just work/power then all you have to know are the basic principles of what work really is, and then how power relates to work...
Did you also have to deal with conservation of energy and such?
Also, being able to manipulate the equations is kind of important...
Work = Force * Distance but also the change in Kinetic Energy... so W = delta KE where KE = 1/2 mass * velocity^2
If you can, provide a specific question you had a problem with, so I can see how they are testing you.

Yes there was conservation energy and nonconservation energy and such...
I was having problems with Power... mainly because I was absent one day during it and never got it down from the *good* teacher... hmm I am moving now... and never got the test back or I would have posted the questions I missed for you guys to work... since

QuotePhysics is fun!

lol.

Edit: I was also having some trouble with... Maybe because I was gone the day of this formula too lol... (Is this even a VALID Equation??)---> Wk=mg(Vf*squared - Vo*squared), Btw anyone know the ALT: for the little 2... (squared)

Quote from: Yoni on February 11, 2004, 01:49 AM

Quote from: Chopz on February 10, 2004, 10:01 PM
Anyone familiar with that shit lol...

Yes.

Quote from: K on February 10, 2004, 10:22 PM
Although this is probably not the right place to post this, since you're not discussing mathemetics per se...

No, it's fine under forum rule 3.4.

Since *Physics* is also related to mathematics then wouldn't it be ok by rule--> 3.1?

Edit: Sorry I double posted there... Should I delete this one and put it in my last post, or is that ok to do if both the replys are under different questions-responses..?

Quote from: Chopz on February 13, 2004, 10:26 PM

Quote from: cipher on February 11, 2004, 04:48 PM
Well, if it was just work/power then all you have to know are the basic principles of what work really is, and then how power relates to work...
Did you also have to deal with conservation of energy and such?
Also, being able to manipulate the equations is kind of important...
Work = Force * Distance but also the change in Kinetic Energy... so W = delta KE where KE = 1/2 mass * velocity^2
If you can, provide a specific question you had a problem with, so I can see how they are testing you.

Yes there was conservation energy and nonconservation energy and such...
I was having problems with Power... mainly because I was absent one day during it and never got it down from the *good* teacher... hmm I am moving now... and never got the test back or I would have posted the questions I missed for you guys to work... since

QuotePhysics is fun!

lol.

Edit: I was also having some trouble with... Maybe because I was gone the day of this formula too lol... (Is this even a VALID Equation??)---> Wk=mg(Vf*squared - Vo*squared), Btw anyone know the ALT: for the little 2... (squared)

I don't think that equation you provided is a valid equation, the only thing I can think of is mass * gravity * height <-> which is gravitational potential energy. KE is as I said 1/2 mass * velocity^2
For the conservation of energy (assuming you're just doing translational conservation of energy) just remember this:
change in KE + change in Gravitational Potential + Change in any others (such as work done by another force, friction, possibly elastic potential energy, or rotational kinetic energy[but we assumed only translational]) always adds up to 0 (conservation of energy) =) If you remember this, and since energy is always converted and never really lost, then changes in potential energy will be offeset by changes in KE or any of those others...
If you use conservation of energy and conservation of momentum, you can do some pretty cool stuff--specifically ballistic pendulums. Ballistic Pendulums are, for example, imagine a block hanging from a light cable that is well attatched to something above it, this block can < --- > (back and forth), and a bullet is being shot at this block. As the bullet hits and becomes lodged into this block (assuming the block is soft enough for this to happen, and not taking into account a few losses of energy such as sound, heat, etc..) conservation of momentum is observed. While the block moves, conversvation of energy is observed and a change in the block's height and knowing various other data can allow one, depending on the provided data, to find out how fast the bullet was traveling when it lodged into the block, or how fast the two traveled after they came together. If you find this interesting I can throw down some equations and explain it conceptually, as it's really a neat problem.  I realize that my description of the problem is probably not adequate so if anyone would like me to draw it out, I wouldn't mind.

Quote from: cipher on February 13, 2004, 11:37 PM
As the bullet hits and becomes lodged into this block (assuming the block is soft enough for this to happen, and not taking into account a few losses of energy such as sound, heat, etc..) conservation of momentum is observed.

Conservation of momentum is observed regardless of sound, heat etc. What might happen is that some momentum is transferred to the air or other things around, but if you ignore the air resistance as the bullet travels, you should ignore the loss of momentum to the air at the impact as well since that's most likely much less.

Quote
(Is this even a VALID Equation??)---> Wk=mg(Vf*squared - Vo*squared)

Quote
I don't think that equation you provided is a valid equation, the only thing I can think of is mass * gravity * height <-> which is gravitational potential energy.

I'll define a system where E = KE + PE. So internal energy such as heat is excluded.

work-energy theorem:
non conservative work = change in mechanical energy

So, Wk = Ef - Ei where 'f' denotes 'final', 'i' denotes initial, and 'Wk' denotes 'non conservative work'.

Wk = (Ekf + Epf) - (Eki + Epi) where 'k' denotes 'kinetic', and 'p' denotes 'potential' (presumably gravity).

Wk = (1/2mVf^2 + mgHf) - (1/2mVi^2 + mgHi)

Consider an instance where there is no change in Ep or Ep is zero. Ep final and initial cancel out or multiply to zero.

Wk = (1/2mVf^2) - (1/2mVi^2)

Factor out the .5 and the (const*)mass.

Wk = 1/2m(Vf^2 - Vi^2)

That what you're lookin for there big shooter ? Somebody else figure out how he got:

Wk=mg(Vf*squared - Vo*squared)