# Friction force of a car rolling down an incline at constant velocity.

## Homework Statement

At a certain part of your drive from home to school, your car (mass m) will coast in neutral at a constant speed of v if there is no wind. Examination of a topographical map shows that for this stretch of straight highway the elevation decreases an amount h for each segment of road of length L. What is the total resistive force (friction plus air resistance) that acts on your car when it is traveling at velocity v?

## The Attempt at a Solution

well I broke the forces down into components. I drew the diagram as a triangle with height h and length L. So, the angle of the hill is arctan(H/L). so then I found the x component of the downward force should be the hypotenuse, mg times sin of the angle of the hill which is arctan(H/L). Well, with this i got mgsin(arctan(h/L) as the force down the hill. So since the total force is zero the resistance must be equal to it in the negative. Well, I'm wrong. I was told "check your trigenometry". I hope someone can explain to me what the flaws in my reasoning were. Thanks alot.

Related Introductory Physics Homework Help News on Phys.org