# Circular motion with an angle

1. Jan 27, 2007

### daniellelok

1. The problem statement, all variables and given/known data
the question is to find the angle that should be banked on a highway curve. the velocity is given, which is 100km/hr and the radius is 300m

2. Relevant equations

3. The attempt at a solution
i know i need to convert the units first, but then i dont know what to do... to find the angle, i need to use tangent to find it, or is it?? if yes, i dont know how...
plz help...tmr is the physics final...thx a lot~~XDXD

2. Jan 27, 2007

### Mindscrape

I can't remember if you end up getting a tangent or not, though you will probably end up with tan or cot. If you draw a careful freebody diagram, and use Newton's 2nd law properly then you can get through this problem.

3. Jan 27, 2007

### daniellelok

the equation i got is that $$\tan\theta=\frac{v^2}{rg}$$. i dont know how i got this equation, but it did give me a right answer. can u help explain it?

Last edited: Jan 27, 2007
4. Jan 27, 2007

### mace2

I think you end up with mgsin0 = mv^2/r
0 = theta

if you draw a freebody diagram you should see that it is that component which creates circular motion. if i'm wrong i apologize but i'm 85% sure. :P

5. Jan 27, 2007

### daniellelok

no...it should be tan, coz i got the right answer from my equation. i just dont understand how i can get the equation on #3

6. Jan 28, 2007

### mace2

i think it depends on where you're counting the angle from.

draw a freebody diagram of the vehicle on the banked turn, the perpendicular component to the car's motion is the Fc. you can write it in terms of Fg and an angle.

7. Jan 28, 2007

### cristo

Staff Emeritus
Where did you get the equation in post 3 from then? What concepts should you use for this question? From these concepts can you attempt to derive the equation?