# AP Physics problem help - centripetal motion

This problem is KILLING ME!!!
The drawing shows a baggage carousel at an airport. Your suitcase has not slid all the way down the slope and is going around at a constant speed on a circle (r = 10.8 m) as the carousel turns. The coefficient of static friction between the suitcase and the carousel is 0.760, and the angle in the drawing is 35.6°. How much time is required for your suitcase to go around once? It involves centripetal motion

#### Attachments

• 13.2 KB Views: 453

Related Introductory Physics Homework Help News on Phys.org
So far here is what I got:

Fc = m*g*tan(theta)
Fn = m*g*cos(theta)
Ffrx (this is x-component of friction) = m*g*cos(theta)*cos(theta)

Ffrx + Fc = (m*w^2) / r

But the answer I get is wrong!

What is the net force acting on the bag? Redo your force diagram.

whozum said:
What is the net force acting on the bag? Redo your force diagram.
Net force is opposite of the perpendicular component of gravity which will be mass times g times cos(theta)
So... Fn = m times 7.968
And Friction will be u times Fn...
Ffr = m times 6.056
And Fc is m times .7159
The x component of Friction will be cos(theta) times Ffr
Ffrx = m times 4.924
And using Ffrx + Fc = (m*w^2) / r
m*4.924+m*.7159 = m*w^2) / r
the mass cancels out and i get
5.64 = w^2 / 10.8
Simplify...
w = .725
Now w = C/T and C= 2*pi*r
.725 / T = 2*pi*10.8
T = .0107

This is still wrong Haha we have that exact same drawing/diagram in our book...you got the book with the skier on it?

I know T must be atleast twenty, but I just cannot get it, please give me a hint!

celticsthree4 said:
Haha we have that exact same drawing/diagram in our book...you got the book with the skier on it?
Ya, Cutnell 5th edition

Let me try this:
w = .725 & C = 21.6*pi
21.6*pi = .725*t
And I get 93.598 for t... somehow that sounds high, but I like someone 2 double check me please

stuplato said:
Let me try this:
w = .725 & C = 21.6*pi
21.6*pi = .725*t
And I get 93.598 for t... somehow that sounds high, but I like someone 2 double check me please
It's wrong AGAIN Doc Al
Mentor
Answer this question: What forces act on the suitcase? (I see three forces.)

Then answer this: What is the net centripetal force?

Answer these questions with symbols, not numbers.

i'm struggling with this same problem except my numbers are a little different my r=11.4, friction is .76 and theta as 36.8.
To be completely honest im in Physics 1 and have no idea how to do physics at all. I understand the concepts, but have a really hard time finding the right equations and right times to use those equations.
I know there are three forces that are acting on it you got the force from the friction pointing up, you have mg acting on the suitcase downwards and you have the N force pulling from the center towards the suitcase.

My teacher in class gave us this equation to solve for the problem:
T= 2 pi sqrt. (R/g)(usin theta +cos theta / ucos theta - sin theta)

I'm not really sure what u= if i knew i think i could solve the problem.
Just to confirm
g=9.8 m/s^2
R=11.4

right?