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))

 

[HalfLostAndSearching]

As a scientist, it is important to understand the concept of acceleration and deceleration as changes in velocity. In this case, the car is initially traveling at a velocity of 10ms-1 and comes to rest, meaning its final velocity is 0ms-1. The negative sign in the equation represents the direction of the acceleration, which in this case is opposite to the initial direction of motion. Therefore, the car is decelerating with a magnitude of 0.625ms-2 and its acceleration vector is pointing in the opposite direction to its initial motion, hence the negative sign. Therefore, the answer is correct and the deceleration of the car is 0.625ms-2 in the opposite direction of its initial motion.