# Homework Help: Banked curve question

1. May 19, 2007

### lzh

QUESTION:A car travels at a speed of 16 m/s around a
curve of radius 21 m.
The acceleration of gravity is 9.8 m/s^2 :
http://img262.imageshack.us/img262/3067/bankedcurvera4.jpg [Broken]
What is the net centripetal force needed to
keep the car from skidding sideways? Answer
in units of N.
if there was no friction, what centripedtal force could be provided just by the banking of the road?
http://img523.imageshack.us/img523/4331/bankrz7.jpg [Broken]
i used 2 eqns for this by dividing all the forces into separate components.
y-direct:
mg+fcos72=ncos18
x-direct:
mv^2/r=nsin18+fsin72
i used those and found
n=32718.5452
f=21413.6627
coeff of frict=.65448
net centripetal=30476.19
i found all of the above for the other parts of the question, and they are all correct. But the question i presented above confused me. If no friction is present, the only force contributing to centripetal force would be the normal force. so that'd be nsin18, but it wasn't right.

what am i thinking wrong here?

Last edited by a moderator: May 2, 2017
2. May 19, 2007

### neutrino

Redo this part.

3. May 19, 2007

### lzh

oh srry about that, i wrote the eqn down wrong, but i did it the right way on paper. its been changed

4. May 19, 2007

### husky88

Yep, that's correct. Maybe there are some other errors in your previous results.

5. May 19, 2007

### lzh

but i know for a fact that my normal force is correct...

6. May 19, 2007

### PhanthomJay

Recalculate the normal force without the friction.

7. May 19, 2007

### lzh

ok, ty, i got it