Frame of reference… if you take the normal to the floor of the car, it would be at an 80* angle to that.
Oh yeah?, so what if the hill is accelerating, eh, smartypants??? 
OK, let me try again:
What are the forces on the yo-yo itself? You should be able to list 3.
Now, the yo-yo is not flying away, so the three forces are balanced, right?
Then you should be able to diagram the three forces, and given that they balance (i.e. the X component adds up to zero, and the Y component adds up to zero), and given the angle, you should be able to solve for all the forces.
(Um, are you sure you don’t want to ask the teacher? Not that I mind answering, but since I have no idea about your current level of understanding or how things were described to you before, I have no idea what kind of hint to give you.)
By the way, if you park the car on a 80-degree incline, pretty soon the car will be accelerating at 9.8 m/s/s…
Not that much more than the real world. The fastest dragsters have a peak acceleration of about 4 g.
Actually, that’s what I got, too, so I think you’re on the right track.
But I have to ask that annoying question: 55.6 what? G’s? m/s[sup]2[/sup]? We’ve been tossing around both of these units, and they differ in size by nearly an order of magnitude. Or is it something else? For the answer to be useful, this detail matters.
Now the real question: Do you understand where that equation you just solved to get 55.6 somethings came from? It sounds like you might not yet, which is perfectly fine. If you don’t, can you hazard a guess?
Actually, this might be even more important: Do you recognize the 9.8 value used in that trig problem? The dimensions have been stripped off, but it’s a number that often comes up in problems involving gravity - when working in a particular system of units. In another common system of units, the same quantity has a numerical value of 32.2…
Unless specified, wouldn’t “normal” be a straight line into the center of the earth? True vertical is vertical, no matter what the car is doing. If the problem specified that the car was allowed to be considered as the horizontal line, not the earth, then yeah that’d work. Otherwise, I go with Chronos.
Cartooniverse, who just spent 4 days describing how masses rotating around a central axis point are manipulated to alter or shift the overall c.g. of the body as a whole to prevent or increase precessing as rotation was introduced into a static body.
Take a gander at The Steadicam Dynamic Balance Primer for a more complete explanation …
Didn’t Einstein say that if you paint the windows of the car black, you couldn’t tell if the angle of the yoyo was due to gravity or acceleration? The angle of the yoyo could even be due to a combination of the two – the car could be accelerating up (or down) a hill.
I audited Physics in H.S. and still failed the Mid-Term. However, I gotta ask- if the windows are painted black, does the cause become irrelevant? If the incline is due to speed or angle and gravity, does it become totally irrelevant? Or is it very important?