# Speed down an incline

how would i find speed down an incline?

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the_d said:
how would i find speed down an incline?
do u mean the speed of a object that was let go from the top of the incline and the speed wanted in the speed of the object at the bottom?
is there friction involved??
Use conservation of energy, it makes things very simple

something like this is generic
$$\Delta K + \Delta U = W_{f} d = \mu F_{N} d$$
where U is the potential energy and Fn is the normal force and mu is the coefficient of friction and d is the length of the ramp. In the absence of friction mu = 0.

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dextercioby
Homework Helper
In general,the theorem of variation of KE is the key...It holds,if inertial forces (like centrifuge,for example) are not present...It deals very well with K friction forces.

Daniel.

the_d said:
how would i find speed down an incline?
Depends on what is given.

First option is to use conservation of total energy in both conservative and non-conservative cases. This is what stunner explained to you.

Second option is to implement the classical newtonian treatment. You start from a chosen frame of reference (usually the x-axis is along the incline) and you determin what forces you have : usually : gravity, friction and the normal force. then apply Newton's second law along both directions and fill in the formula's for position and velocity as a function of time, along each direction.

marlon

dextercioby
Homework Helper
marlon said:
(...)conservation of total energy in both conservative and non-conservative cases.(...)
In the mildest case,that could be considered an oxymoron.Conservation of energy is appliable for conservative forces,only...So your "nonconservative cases" sounds really dubious.

Daniel.

dextercioby said:
In the mildest case,that could be considered an oxymoron.Conservation of energy is appliable for conservative forces,only...So your "nonconservative cases" sounds really dubious.

Daniel.
Maybe to you, but what the heck... who cares ?

marlon

dextercioby
Homework Helper
Thank God you're not doing a PhD in classical Newtonian mechanics...Ergo,nobody cares.

Daniel.

dextercioby said:
Thank God you're not doing a PhD in classical Newtonian mechanics...
Daniel.
What a mature post dexter, it's getting better by the minute.

Why are you always talking about my PhD ???

Are you....errr...?

marlon

dextercioby
Homework Helper
You make fuss of it...You show many gaps for a PhD stud.,but i guess that's the rule in Belgium.I've seen a PhD stud at KUL who had no idea about functional derivatives.He had never heard of Fréchet and Gâteaux derivatives,yet he was trying to explain to the students how to derive Euler-Lagrange eqns...That's sad.

Daniel.

dextercioby
Homework Helper
And one more thing.Compassion and empathy are not envy.

Did i mention that

"I really wish you good luck with the thesis" ?

Daniel.

dextercioby said:
You show many gaps for a PhD stud.,but i guess that's the rule in Belgium.

I've seen a PhD stud at KUL who had no idea about functional derivatives.He had never heard of Fréchet and Gâteaux derivatives,yet he was trying to explain to the students how to derive Euler-Lagrange eqns...That's sad.

Daniel.
I don't believe you. Besides regurgitating posh sounding names does not qualify as real physics dexter. that's why YOU are not fit for a PhD anywhere :rofl:

Ps Gâteaux derivatives :rofl: :rofl: what a big joke, just call it directional derivative, OK ?

Besides, the incline question from yesterday was correct. I challenge you to point out any mistake apart from the mass m that i should have left out. But that is NOT what you pointed out to be wrong. I am referring to initial velocity and position...

marlon

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dextercioby
Homework Helper
If you were to discover something one day (by accident,or by work,or even by absurd),wouldn't u like to be remembered for that?

Why do we call them Lagrange eqns. and not "the ODE-s that come out when imposing Gâteaux derivative of the Lagrangian action equal to 0,under certain boundary conditions ?"...Don't tell me it's shorter.It's FAIR.Lagrange found them.Not by this method,of course,but he found them.

Daniel.

dextercioby said:
If you were to discover something one day (by accident,or by work,or even by absurd),wouldn't u like to be remembered for that?

Why do we call them Lagrange eqns. and not "the ODE-s that come out when imposing Gâteaux derivative of the Lagrangian action equal to 0,under certain boundary conditions
Daniel.
This is a perfect example of what i am trying to say. I am convinced that you prefer to second name, yet it is completely worthless. Indeed Lagrange found out these equations but the 'method' in the second name is certainly NOT essential to these equations.I can assure you, one can derive the Euler Lagrange equations without whining about this Gâteaux rubbish. You see, don't complain if somebody does not know a concept in that specific formulation and don't complain about a concept that is NOT fundamental within a certain context. if you keep working like this, you will find yourself complaining about everything. You, yourself don't do anything, you just complain about others, yet it's 'the others' that do all the work. You are no physicist dexter, you are a bad historian,...That's not an insult, it's the truth...I really wonder what you do there at the KUL, though i have my doubts whether you are really following all these subjects of the fourth year.

regards
marlon

dextercioby
Homework Helper
May i add,future professor Nikolaas,that i really hope u won't bump into a student like me one day,i student who'd show his teacher the gaps in his (professor's) preparation...?

Daniel.

dextercioby said:
May i add,future professor Nikolaas,that i really hope u won't bump into a student like me one day,i student who'd show his teacher the gaps in his (professor's) preparation...?

Daniel.
No, no,no, again you got it all wrong. i'd be more then glad if someone points out the gaps in my preparation. It's just that your actual 'pointing out' is incorrect 95% of the times. THAT is the point, which you don't seem to get.
If i'd have i student like you, i'd be spending most of my time correcting this person's wrong views. But isn't that what teaching is all about, Daniel ?

marlon

dextercioby
Homework Helper
In that eenie-weenie 5% i guess we can add setting acceleration equal to force,then?And those traceless SU(3) matrix?

Daniel.

dextercioby said:
In that eenie-weenie 5% i guess we can add setting acceleration equal to force,then?And those traceless SU(3) matrix?

Daniel.
Agreed, same goes for yourself plus the 'Galilei-formula' , plus vacuum fluctuations and we end by a marvellous syntaxis-capability...

regards
marlon

dextercioby
Homework Helper
Mr.$APXIMN\Delta N \Sigma$,it's SYNTAX...

And what's with Galilei's formula?Are u claiming that it doesn't hold? :surprised

Daniel.

dextercioby said:
Mr.$APXIMN\Delta N \Sigma$,it's SYNTAX...

Daniel.
Good point amigo. i was NOT referring to that...Do i need to provide you with a link ???

marlon

dextercioby
Homework Helper
You mentioned my "marvelous syntaxis (sic!)-capability".Yet,right in this very syntagma you gave a "marvelous" proof of your wonderful spelling-capability.

I'm running low on inspiration today.So excuse me for paraphrasing you,but i ran outta ideas...:tongue2:

Daniel.

dextercioby said:
I'm running low on inspiration today.
So i have noticed. Don't worry, i know that happens a lot to you

regards
marlon

dextercioby
Homework Helper
The refreshing part is that i don't sweat either...That would have really been frustrating,99% of a genius...:tongue2:

Daniel.

Get a room...

:P

i used the formula (1/2)mv1^2 + mgy1 = (1/2)mv2^2 + mgy2 and just solved for v2^2 to solve a question involving speed down an incline, but i am not getting the correct answer, can i do this?

dextercioby