Maxim velocity at the top of the loop (rollercoaster pb)

[shuby]

Homework Statement

What's the MAXIMUM velocity the roller coaster should have at pt A in order for the passengers to stay in contact with their seats ?
calculate the velocity for r=7

It kinda looks like this
[img=http://img94.imageshack.us/img94/6994/image39.gif]

Homework Equations

The Attempt at a Solution

The friction is not mentioned anywhere, so let's forget about it, i thought that it has something to do with the normal force, so it should be like this:
Nmax + mg = mv^2/r

does it need some advanced stuff about the normal force to solve this?
does it have something to do with friction between the passenger and the seat ?

Thanks for clearing this up for me, and sorry for my poor English.

 

[lewando]

Your English is fine. Friction between passenger and seat is nor relevant. At point A, what forces are acting on the passenger?

 

[shuby]

Normal and gravitational force(mg)

Usually we want to know what's the minimum velocity so that the can make it (N>0) but here I don't understand the question, what happens if it's going too fast ? will the rail break ? if yes what does that mean ?

 

[RoyalCat]

Normal and gravitational force(mg)

Usually we want to know what's the minimum velocity so that the can make it (N>0) but here I don't understand the question, what happens if it's going too fast ? will the rail break ? if yes what does that mean ?

Unless you're taking a course on structural engineering, that's irrelevant. :P

I think your question was worded poorly. It should have said, MINIMUM velocity, since the only maximum there is to consider is the strength of the materials involved, which is completely out of the scope of the data of the question.

 

[shuby]

Yeah that's what I thought when I saw the question, but then I said maybe I'm wrong since the problem has 3 questions : a)what's the minimum V b)maximum V c)calculate the value for r=7

It's a instructor made problem... :p

Thanks for the help ! and I guess you will often see me in this board in the future, maybe not in this sub forum because I'll be in Electrical Engineering next year.