1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Acceleration and speed as m*s^-1

  1. Jan 23, 2014 #1
    I was given this question today and I have never seen acceleration or speed with a minus power in the unit (m/s^-2). Also speed in the question has a ^-1 in the unit and I thought the unit for speed was m/s (meters per second)


    1. The problem statement, all variables and given/known data

    A body starts from rest and is subject to a constant contant acceleration of 4ms^-2 up to a speed of 20ms^-1. It then travels 20ms^-1 for 30 seconds after witch time it is retarded to a speed of 4ms^-1, if the complete motion takes 50 seconds, Find:

    A) The time taken to reach 20ms^-1.

    B) The retardation.

    C)Total distance travelled.


    2. Relevant equations



    3. The attempt at a solution

    I have know idea what these strange units mean.
     
  2. jcsd
  3. Jan 23, 2014 #2

    DrClaude

    User Avatar

    Staff: Mentor

    Hi Xecutive. Welcome to PF!

    It is simply standard algebra applied to units (which should be treated as mathematical objects).

    $$x^{-1} = \frac{1}{x}$$

    $$\mathrm{m} \; \mathrm{s}^{-1} = \frac{\mathrm{m}}{\mathrm{s}}$$

    $$\mathrm{m} \; \mathrm{s}^{-2} = \frac{\mathrm{m}}{\mathrm{s}^2}$$

    Note that it is not ##\mathrm{m} / \mathrm{s}^{-1}##, but ##\mathrm{m} \; \mathrm{s}^{-1}##. The former would give
    $$
    \mathrm{m} / \mathrm{s}^{-1} = \frac{\mathrm{m}}{\mathrm{s}^{-1}} = \mathrm{m} \; \mathrm{s}
    $$
     
  4. Jan 23, 2014 #3

    PhanthomJay

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    you mean ms^-2 not m/s^-2
    yes, the unit for speed is m/s, and m/s can be writen as ms^-1.....it's just taking the denominator, s, and placing it in the numerator as s^-1.
    I personally would rather see it written as m/s instead of ms^-1, but they are nevertheless mathematically the same unit, just an algebraic manipulation of the variables.

    Welcome to these forums!
     
  5. Jan 23, 2014 #4
    It seems so obvious now.

    Thanks.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Acceleration and speed as m*s^-1
  1. Speed and acceleration (Replies: 9)

  2. Speed and acceleration (Replies: 1)

  3. Acceleration and speed . (Replies: 16)

  4. Speed and acceleration (Replies: 2)

Loading...