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Thread: Acceleration calculation - what am I doing wrong?

  1. #1
    Join Date
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    Acceleration calculation - what am I doing wrong?

    I am trying to figure out how to use the formula for calculating acceleration.

    First try:
    Initial speed - 0 metres/s^2
    Final speed - 100 metres/s^2
    Time - 10 seconds.
    Answer - 10 meters/s^2
    Follow up question: How many g's is 10 meters/s^2?
    Answer is 10 meters/s^2/9.8 meters/s^2= 1.0204 g's.

    Second try:
    Initial speed - 0 metres/s^2
    Final speed - 1,000,000 metres/s^2 (1,000 KM)
    Time - 1000 seconds.
    Answer - 1000 meters/s^2
    Follow up question: How many g's is 1000 meters/s^2?
    Answer is 1000 meters/s^2/s^2/9.8 meters/s^2 =102.04 g's.

    Am I doing this correctly?
    Something "feels" wrong about this and I have no idea what it could be.
    Solfe

    -----------------------------------------------------------------------------------
    "You're only given one little spark of madness. You mustn't lose it." Robin Williams.

  2. #2
    Join Date
    Jan 2002
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    922
    appears to be correct Solfe...
    Rememebr to always start with the formula and simply plug in the knowns and solve for the unknown.

    V(f) - V(i) = at
    100 m/sec - 0 = (a)(10 sec)
    Now solve for a.


  3. #3
    Join Date
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    Quote Originally Posted by Solfe View Post

    Final speed - 100 metres/s^2

    ::snip::

    Am I doing this correctly?
    Something "feels" wrong about this and I have no idea what it could be.
    Maybe it's the speed in metres/s^2 instead of metres/s

  4. #4
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    Quote Originally Posted by grapes View Post
    Maybe it's the speed in metres/s^2 instead of metres/s
    I was doing this on paper, so I think you are right. I was writing the wrong terms.

    I will get the hang of this someday.
    Solfe

    -----------------------------------------------------------------------------------
    "You're only given one little spark of madness. You mustn't lose it." Robin Williams.

  5. #5
    Join Date
    Aug 2007
    Posts
    214
    Quote Originally Posted by Solfe View Post
    I am trying to figure out how to use the formula for calculating acceleration.

    First try:
    Initial speed - 0 metres/s^2
    Final speed - 100 metres/s^2
    Time - 10 seconds.
    Answer - 10 meters/s^2
    Follow up question: How many g's is 10 meters/s^2?
    Answer is 10 meters/s^2/9.8 meters/s^2= 1.0204 g's.

    Second try:
    Initial speed - 0 metres/s^2
    Final speed - 1,000,000 metres/s^2 (1,000 KM)
    Time - 1000 seconds.
    Answer - 1000 meters/s^2
    Follow up question: How many g's is 1000 meters/s^2?
    Answer is 1000 meters/s^2/s^2/9.8 meters/s^2 =102.04 g's.

    Am I doing this correctly?
    Something "feels" wrong about this and I have no idea what it could be.
    Hello Solfe,

    there's a wrong unit in your initial variables:

    #1 Speed (i.e. velocity) is expressed in distance per time. E.g Miles per hour or metres per second (m/s). Accelerations, i.e. change of velocity over time, is therefore expressed as distance per times squared: (m/s^2)
    #2 As acceleration is change of velocity over time one can write: a = v/t. Solving for v this yields : v = a*t. So simply multiply your acceleration with time and you'll get your final speed.

    Ex

    P.S.
    A more general equation is a = ^v/^t. Acceleration equals change of velocity in a certain tie period. Therefore: a = (v2-v1)/(t2-t1)

  6. #6
    Join Date
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    Or in distance terms v^2 = u^2 + 2.a.s where a is acceleration and s distance in consistent units. u is the starting speed.
    the link from distance to time is s= u.t + 1/2. a.t^2

  7. #7
    Join Date
    Apr 2004
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    1,804
    FYI, you are dealing with constant accelerations. Whilst motion under gravity tends to have constant acceleration, mechanical devices like cars tend not to have constand accelrations.

    So a sports car that does 0-60mph in 5 seconds has a average acceleration of about 12mph per second (a rather mixed unit, but it helps understand the principle), in practice its accleration will not be constant, and the distance it travels will not be precisely half-a-t-squared.

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