Results 1 to 3 of 3

Math Help - Motion equations

  1. #1
    Newbie
    Joined
    Mar 2008
    Posts
    1

    Unhappy Motion equations

    Hi all,
    Im new to the forum .

    I am writing a application that displays predicted quarter mile preformance of cars based on power and weight.
    I am attempting to add a visual display of the acceleration of the car. I have been using suvat equations but for some reason i cant seem to get the desired results (maybe because the car doesnt have a constant accelerations?).

    given the following data:

    distance = 402m
    start speed = 0
    end speed = 147mph / 65.71ms
    acceleration = ???
    time = 10 seconds

    now for some reason, whenever i put the forumula into my program(or even on paper) the distance ends up as ~700m. and the time is usually much quicker than 10seconds??!?!

    Im sure it must be something i am doing wrong. see my working below:
    *************************

    distance = startspeed*time + 0.5*a*t^2
    dis = 403 (quartermile)

    .: 403 = 0.5*a*10^2
    .: 403/100 = 0.5*a
    .: 4.03/0.5 = a
    .: a= 8.6??????

    *************************

    endspeed = startspeed + at
    .: 147 = 0 + a*10
    .:147/10 = a
    .: a= 14.7ms????

    *************************

    endspeed^2 - startspeed^2 = 2*a*d
    .: 21609 - 0 = 2*a*403
    .: 21609/2 = a*403
    .: 10804.5/403 = a
    .: a= 26.81

    *************************

    SO
    As you can plainly see, i am no mathamitican.
    i get 3 completely different valuse for acceleration?!?!

    To summerise, what i want to be able to do is get the total distance traveled at intervals of say 0.1 seconds using the data provided.
    I know the car doesnt have constant acceleration but surly it can be converted into a constant accleration.

    Thanks again
    Neil.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Forum Admin topsquark's Avatar
    Joined
    Jan 2006
    From
    Wellsville, NY
    Posts
    9,846
    Thanks
    321
    Awards
    1
    Quote Originally Posted by hopoffbaby View Post
    Hi all,
    Im new to the forum .

    I am writing a application that displays predicted quarter mile preformance of cars based on power and weight.
    I am attempting to add a visual display of the acceleration of the car. I have been using suvat equations but for some reason i cant seem to get the desired results (maybe because the car doesnt have a constant accelerations?).

    given the following data:

    distance = 402m
    start speed = 0
    end speed = 147mph / 65.71ms
    acceleration = ???
    time = 10 seconds

    now for some reason, whenever i put the forumula into my program(or even on paper) the distance ends up as ~700m. and the time is usually much quicker than 10seconds??!?!

    Im sure it must be something i am doing wrong. see my working below:
    *************************

    distance = startspeed*time + 0.5*a*t^2
    dis = 403 (quartermile)

    .: 403 = 0.5*a*10^2
    .: 403/100 = 0.5*a
    .: 4.03/0.5 = a
    .: a= 8.6??????

    *************************

    endspeed = startspeed + at
    .: 147 = 0 + a*10
    .:147/10 = a
    .: a= 14.7ms????

    *************************

    endspeed^2 - startspeed^2 = 2*a*d
    .: 21609 - 0 = 2*a*403
    .: 21609/2 = a*403
    .: 10804.5/403 = a
    .: a= 26.81

    *************************

    SO
    As you can plainly see, i am no mathamitican.
    i get 3 completely different valuse for acceleration?!?!

    To summerise, what i want to be able to do is get the total distance traveled at intervals of say 0.1 seconds using the data provided.
    I know the car doesnt have constant acceleration but surly it can be converted into a constant accleration.

    Thanks again
    Neil.
    You are doing nothing wrong in your calculations. I would strongly suspect that the error is in using the SUVAT equations at all. There is no reason to expect that a car will maintain a constant acceleration over the 10 second period.

    What I would do is plot a graph of speed vs. time. That way you can calculate the acceleration over small time intervals. It'll be messy and involve calculus before you are done, but its doable.

    -Dan
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Super Member
    earboth's Avatar
    Joined
    Jan 2006
    From
    Germany
    Posts
    5,829
    Thanks
    123
    Quote Originally Posted by hopoffbaby View Post

    ...
    given the following data:

    distance = 402m
    start speed = 0
    end speed = 147mph / 65.71ms
    acceleration = ???
    time = 10 seconds
    ...
    Im sure it must be something i am doing wrong. see my working below:
    *************************

    distance = startspeed*time + 0.5*a*t^2
    dis = 403 (quartermile)

    .: 403 = 0.5*a*10^2
    .: 403/100 = 0.5*a
    .: 4.03/0.5 = a
    .: a= 8.6?????? ....... OK

    *************************

    endspeed = startspeed + at
    .: 147 = 0 + a*10 ....... endspeed = 65.71 m/s
    .:147/10 = a
    .: a= 14.7ms????

    *************************

    endspeed^2 - startspeed^2 = 2*a*d
    .: 21609 - 0 = 2*a*403
    .: 21609/2 = a*403
    .: 10804.5/403 = a
    .: a= 26.81

    *************************

    ...
    To cover a quarter mile in 10 s you need an acceleration of 8.6 m/sē.

    The given data show that the car has an acceleration of a = 6.57 m/sē.

    So don't believe the driver - he is exaggerating as allways!
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Modeling motion using parametirc equations?
    Posted in the Trigonometry Forum
    Replies: 1
    Last Post: April 2nd 2011, 10:57 AM
  2. [SOLVED] Equations of Motion
    Posted in the Math Topics Forum
    Replies: 2
    Last Post: May 17th 2010, 04:39 AM
  3. [Help Me!] Linear motion equations with drag resistance
    Posted in the Advanced Applied Math Forum
    Replies: 3
    Last Post: September 25th 2009, 10:08 AM
  4. Plane motion w/ parametric equations
    Posted in the Calculus Forum
    Replies: 2
    Last Post: May 13th 2009, 05:53 PM
  5. Replies: 1
    Last Post: February 19th 2009, 02:30 PM

Search Tags


/mathhelpforum @mathhelpforum