Quantum Physics

please! I need help now!

Okay Norc, your physics teacher is here (his real job is less important and fun than this).

Work through this in steps.

what variables do you have in the problem? (a, t, d, Vo, Vf)
You will notice that none of your equations have exactly this combination! What's a poor Norc to do?
First, which of these values are known (a, t, d) and which are unknown (Vo, Vf)
You are asked to find TWO unknowns.
Can any ONE equation be solved to provide TWO unknowns?
AHA!
How many equations do you need?

Now that we have dealt with that conceptual hurdle, if you have two equations and two unknowns, how do you proceed? make one unknown disappear by substitution, then algebrate to find the other unknown. Now go backwards to find the first unknown you eliminated.

ps: if you substitute in numbers before solving algebraically, I will be very disappointed. Keep the algebra symbolic until you have solved for the unknown! Only this way will your skills grow.

Actually you can get the first one without any algebraic substitution, but I'll let you find it.

thank you very much, but what equation should I use? I know a (acceleration) = 3.2, i know t (time) 2.5 second and I know distance s 45 m. "Start" speed Vo and "end" speed V.

which equation has one of your two unknowns with all the other variables known?

I'm assuming you have the full set, if not you will have to find two equations that have both unknowns and do some substitution.

FOUND IT OMG! (i hope)
S=Vot+1/2at^2

s=distance. 1/2 means a half and ^means it's like lifted. is that the equations?

you two are scarily brainy

no it's not it. I get 35, it's supposed to be 22 and 14 I think.

Norc wrote:FOUND IT OMG! (i hope)
S=Vot+1/2at^2

s=distance. 1/2 means a half and ^means it's like lifted. is that the equations?

Yes, that's the one that will give you the part of the change of distance due to the acceleration. Be careful not to forget about the - sign.

wait! do I have to like V(t) = s´(t)

That's just the calculus definition of velocity. You should have a number of equations that use constant acceleration. Should be about 4 of them. Given this problem, I'd expect you'd been using them for the last week in class.

Wait, do you know calculus? You could use it but it will take longer than using the set of constant acceleration equations.

i don't know if I use calculus... but how.. concstant acceleration, like
V=Vo + at
and
s=1/2(Vo+V)t
and
s=Vot+1/2at^2
and
v^2=Vo^2+2as ?

yep, those are them. Now just find one that has one unknown and everything else is known, and you are on your way.

but I have two unknowns!

I get 8 which is wrong. i'm supposed to get 22... gawd... what do I do wrong!!

you know what Halfwise, thank you very very, much for your help, I really appreciate you taking your time helping me, but I think I need some sleep before I can tackle this problem again. I'm gonna do more tomorrow after school. I'll try again then. You've actually helped me alot, i think i know vaguely what I'm gonna do, I just can't get it to work.. well, anyways. thanks. and good night.

Or did you have acceleration positive? If moving forward and slowing down, what should the acceleration be?

I just saw a bunch of messages I missed like at the bottom of pages and things with david pitching in - we are basically saying the same things.

Anyway, as we have both said, check the sign of acceleration. This is the main thing new physics students get wrong. If it confuses you we will have to give you some vector lessons.

And you deal with one unknown at a time.

Bloody hell I know nothing!

Not quantum, well it probably is buts thats another discussion, but iti sis ciency- some stuff on the human genome project.

'Scientists have published the most detailed analysis to date of the human genome.
They've discovered a far larger chunk of our genetic code is biologically active than previously thought.
The researchers hope the findings will lead to a deeper understanding of numerous diseases, which could lead to better treatments.
More than 400 scientists in 32 laboratories in the UK, US, Spain, Singapore and Japan were involved.
A pilot project looking at 1% of the genome was published in 2007.
Now the Encode project has analysed all three billion pairs of genetic code that make up our DNA.
They have found 80% of our genome is performing a specific function.
Up to now, most attention has been focused on protein-coding genes, which make up just 2% of the genome.
The Encode team analysed the vast area of the genome sometimes called "junk DNA" because it seemed to have little function and was poorly understood.
Dr Ewan Birney, of the European Bioinformatics Institute in Cambridge, who led the analysis, told me: "The term junk DNA must now be junked.
"It's clear from this research that a far bigger part of the genome is biologically active than was previously thought."
The scientists also identified four million gene "switches". These are sections of DNA that control when genes are switched on or off in cells.
They said the switches were often a long way along the genome from the gene they controlled.
Dr Birney said: "This will help in our understanding of human biology. Many of the switches we have identified are linked to changes in risk for conditions from heart disease to diabetes or mental illness. This will give researchers a whole new world to explore and ultimately, it's hoped, will lead to new treatments."- BBC

Its hard to imagine the possible discovers and abilities this sort of understanding might one day give to humans.

Yeah, I remember when they first discovered 'junk' DNA. Little did they know....

So did you get it, Norc?

Where is that dratted little Norclet anyway?