# Confused on homework problem

## Homework Statement

A 2450 kg car traveling to the west at 16.4 m/s slows down uniformly under a force of 8930 N to the east.
a) How much force would be required to cause the same acceleration on a car of mass 3170 kg? Answer in units of N.

## The Attempt at a Solution

I found in the first cart 2450x16.4 = 40,180 kg*m/s (the momentum)
Since 8930 N is the same as 8930 kg*m/s^2
40,180 / 8930 = 4.49900449 seconds

I tried to use a similar with the second cart 3170 kg, but the problem is I don't know the force since i'm trying to find it I got stuck.

## Answers and Replies

gabbagabbahey
Homework Helper
Gold Member
4.49....s is the time it takes for the car to decelerate to a stop not the value of its acceleration.....dont you want to use F=ma for this question? ;0)

That's what I thought too gabba, but then figured I was wrong to having it be a question.

F = ma
(-)8930 = 2450a
a = -3.64 m/s^2

F = ma
F = (3170)(3.64 m/s^2)
F ≅ 11,554 N

gabbagabbahey
Homework Helper
Gold Member
Looks good to me...the fact that they told you the initial speed was meant to throw you off.

O I see I totally misread the question..... yea the intial speed threw me off.... i under stand it now. thanks a lot!!!