# Unbalanced force

## Homework Statement

A car has a mass of 1350 kg and an initial speed of 21 m s-1. Calculate the magnitude of the unbalanced force applied to the brakes that caused the car to come to a halt in 3 seconds.

## Homework Equations

Force = mass x acceleration,
= ( 1350 kg ) x ( -7 m s-2 ),
= -9450 kg m s-2
= -9450 N

My question is this, is it ok to write the answer as a negative value of newtons, as above, because it doesn't seem right? I'm a little confused, any advice would be appreciated.

## The Attempt at a Solution

Doc Al
Mentor
My question is this, is it ok to write the answer as a negative value of newtons, as above, because it doesn't seem right? I'm a little confused, any advice would be appreciated.
Magnitudes are always positive. In this case, the negative sign just indicates the direction--that the acceleration and force were opposite to the velocity.

Magnitudes are always positive. In this case, the negative sign just indicates the direction--that the acceleration and force were opposite to the velocity.

so

Force = mass x acceleration,
= ( 1350 kg ) x ( -7 m s-2 ),
= -9450 kg m s-2
= 9450 N

would be correct?

Doc Al
Mentor