# Homework Help: Help with Forces

1. Feb 25, 2006

### ant124m

I need help with this question:

A 1600.3 kg car is traveling at 26.4 m/s when the driver takes his foot off the gasd pedal. It takes 4.5 s for the car to slow down to 20 m/s. How large is the net force slowing the car? Answer in units of N.

I suck with forces and I have no idea how to do this. Can someone please help me out?

2. Feb 25, 2006

### topsquark

To get a force you need an acceleration. How might you find an acceleration for the problem?

-Dan

3. Feb 25, 2006

### ant124m

Would I have to use the formula v = v0 + at?

4. Feb 25, 2006

### topsquark

Sounds good to me!

-Dan

5. Feb 25, 2006

### ant124m

But what would v equal since I am given two velocities?

6. Feb 25, 2006

### anjor

basic defintions

u stated the right formula...
just go to the basics..
what is acceleration?? it is the rate of change of velocity.
The two velocities given to you are for two different instances of time.
Hope that helps.

7. Sep 22, 2006

### jareyn3

Can someone please provide a little more help for this problem, I have a very similar problem and I am stumped. Can you use a= Vo-Vf/t and then use the formula F=ma to get the force???

8. Sep 22, 2006

Of course. But it looks more like $$a = \frac{v_{f}-v_{0}}{t}$$.