Why Is Deceleration Expressed as a Positive Value in Physics Problems?

[TheShiny]

Homework Statement

"A car is approaching traffic lights. The car is traveling with speed 10ms^-1. The driver applies the brakes to the car and the car comes to rest with constant deceleration in 16s. Modelling the car as a particle, find the deceleration of the car."

Homework Equations

v = u + at

The Attempt at a Solution

[STRIKE]s =[/STRIKE], u = 10ms^-1, v = 0ms^-1, a = ?, t = 16s

v = u + at
0 = 10 + 16a
a = -10 ÷ 16
a = -0.625ms^-2

The answer given is 0.625ms^-2. Why is the answer positive and not negative?

 

[TheShiny]

If the particle (the car) is slowing down it would have negative acceleration.

So, to go from acceleration to deceleration multiply by -1.

Therefore the deceleration would be -1 * -0.625 = 0.625

Is that why the answer is positive or have I misunderstood?

 

[lendav_rott]

The car's acceleration is -0.625 units, its deceleration is 0.625 units :) Game of words
You have understood correctly.

 

[adjacent]

As lendav_rott said,
Negative acceleration is simply deceleration and | positive acceleration can be negative deceleration(Can be,but this is rarely used or never used(in my experience))