# A car on black ice is on a banked road

1. Jun 21, 2013

### x86

1. The problem statement, all variables and given/known data
A stationary car on black ice (no friction) is on a banked road and begins to experience some acceleration. What force is causing the acceleration?

a) The horizontal component of the normal force
b) The vertical component of the normal force
c) Gravity

2. Relevant equations

3. The attempt at a solution
This confused me, because the answer is clearly gravity (gsinx) but the horizontal component of the normal force also does make sense.

So is the answer a or c? From my understanding the normal force is only a reaction force... but it does make sense; say the normal force is applied at some angle; then isn't it possible for its x or y components to cause acceleration?

I'm not sure which is correct for bank turns, because i've learned that the horizontal component is from gravity (gsinx) but some websites say its the normal force (Nsinx). What would be the force in this scenario?

Last edited: Jun 21, 2013
2. Jun 21, 2013

### haruspex

In my view it's the resultant of all 3. Do you have to pick one?
If I had to pick one I'd say gravity, on the basis that the normal force is orthogonal to the direction of acceleration.

3. Jun 21, 2013

### x86

Yes we have to pick one. It's a high school physics course so I guess gravity doing it would be enough

4. Jun 21, 2013

### dreamLord

I would say gravity as well.