Why is the stopping acceleration positive when a car brakes to a stop?

[Frankenstein19]

Homework Statement

Calculate the acceleration of a 1400kg car if it can stop from 35km/h (9.72m/s) on a dime (diameter= 1.7cm) (0.017m). What is the force felt by the 68kg occupant of the car?

Homework Equations

v^2=v0^2+2a(x-x0)
F=ma

The Attempt at a Solution

ok after solving for a in that equation i get -2779m/s^2. when i go to calculate the force felt by the 68kg constituant, i'd just plug everything in, which would mean i'd get a negative force. the back of my book says that the answer is correct but instead of it being negative like i have it it is positive. WHY? why was the acceleration changed?

 

[axmls]

It's difficult to tell without having the book, but it's likely that it was simply looking for the magnitude of the force, which would be positive.

 

[Frankenstein19]

It's difficult to tell without having the book, but it's likely that it was simply looking for the magnitude of the force, which would be positive.

the books question

the answer

 

[axmls]

Yes, it looks like they're just looking for the magnitude of the force.