- #1

anne921

- 10

- 0

## Homework Statement

A 2.1 X 10^3 kg car starts from rest at the top of a driveway that is sloped at an angle of 20.0 degrees with the horizontal. An average friction force of 4.0 X 10^3 N impedes the car's motion so that the car's speed at the bottom of the driveway is 3.8 m/s. What is the length of the driveway?

## Homework Equations

Wnet - ΔKE = KEf - KEi

Wnet = Fd cos θ

Fnet = mgsinθ - Fk

## The Attempt at a Solution

I understand the basic idea of how to solve this problem. I think I would calculate Wnet using 1/2 mvf^2 (vi = 0); solve for Fnet and then substitute these values into solve for d by rearranging Wnet = Fdcosθ. My problem is that the key defines two angles - θ and θ'; with θ=20 degrees and θ' = 0. I don't understand where θ' comes into the picture. I am a Chemistry teacher trying to teach an intro physics course and I need some concrete help!