# Centripetal force and friction

1. Feb 4, 2005

### shwoll

I have been having trouble with this problem for quite awhile now, and im wondering if anyone could offer some help...

I figured out part one...that the x direction forces must equal each other (mg sin theta = m*v^2/R) but i am completely lost on the second part. Number 6. Thanks!

5. [1pt]

Correct, computer gets: 1.30E+02 mi/hr

6. [1pt]

2. Feb 4, 2005

### Staff: Mentor

Newton's 2nd Law

Not so fast. The forces in the x-direction must add up to equal $m a_c = m v^2/r$. What forces act on the car? In the "no friction" case, there are only two forces. Friction adds a third force. (Which way does the friction act?)

You'll also need to realize that vertical forces are in equilibrium.