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Deceleration of a particle

  1. Feb 19, 2014 #1
    1. The problem statement, all variables and given/known data
    "A car is approaching traffic lights. The car is travelling 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."

    2. Relevant equations
    v = u + at

    3. 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?
  2. jcsd
  3. Feb 19, 2014 #2
    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?
  4. Feb 19, 2014 #3
    The car's acceleration is -0.625 units, its deceleration is 0.625 units :) Game of words
    You have understood correctly.
    Last edited: Feb 19, 2014
  5. Feb 19, 2014 #4


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    Gold Member

    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))
    Last edited: Feb 19, 2014
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