# Homework Help: Work-Energy Method

1. Oct 31, 2007

### Heat

[SOLVED] Work-Energy Method

1. The problem statement, all variables and given/known data

A car is stopped by a constant friction force that is independent of the car's speed. By what factor is the stopping distance changed if the car's initial speed is doubled? (Solve using work-energy methods.)

2. Relevant equations

Wtotal = delta K

3. The attempt at a solution

From what the problem is stating, is that friction force, is seperate from car's speed.
''if the car's initial speed is doubled?''
K1 = 1/2(m)(2v)^2

I know the answer is 4, but I don't comprehend, what is the car's initial speed is tripled, would it be 6?

2. Oct 31, 2007

### Staff: Mentor

How does stopping distance relate to kinetic energy?

3. Oct 31, 2007

### Heat

well if the velocity is higher, then it would be harder to stop at a shorter distance than a long one.

4. Oct 31, 2007

### Staff: Mentor

I'm looking for a precise answer. What factors affect stopping distance? Give an equation.

5. Oct 31, 2007

### Heat

well

W = F*s

s being distance

and work total = k2-k1

so, k2-k1 = F*s