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Math Help - how to calculate final velocity of car

  1. #1
    Member moonnightingale's Avatar
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    how to calculate final velocity of car

    If a car accelerates uniformly from rest at 3.2m/s(2). when the car has traveled a distance of 40. meters, its speed will be.

    I tried to use equation

    v-u/a= t

    but there r two unknowns in this

    t and v...

    how to solve it
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  2. #2
    Member moonnightingale's Avatar
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    Re: how to calculate final velocity of car

    Ok i have solved in this way

    since S=vt, so t=S/v

    Equating both equations

    v-u/a= S/v

    v/3.2=40/v

    v(2) = 128

    v= 11.31 m/sec

    is this approach correct
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  3. #3
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    Re: how to calculate final velocity of car

    Quote Originally Posted by moonnightingale View Post
    If a car accelerates uniformly from rest at 3.2m/s(2). when the car has traveled a distance of 40. meters, its speed will be.

    I tried to use equation

    v-u/a= t

    but there r two unknowns in this

    t and v...

    how to solve it
    You're expected to be familiar with the uniform acceleration straightline motion formulae. I sugest you go back to your class notes or textbook and review this topic more thoroughly.

    For the question you posted, use 2as = v^2 - u^2, substitute the given data and solve for v.
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  4. #4
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    Re: how to calculate final velocity of car

    Quote Originally Posted by moonnightingale View Post
    Ok i have solved in this way

    since S=vt, so t=S/v

    Equating both equations

    v-u/a= S/v

    v/3.2=40/v

    v(2) = 128

    v= 11.31 m/sec

    is this approach correct
    No, it is not because the formula v= S/t applies only to constant velocities.

    Rather, use v= at and [/tex]S= (1/2)at^2[/tex]. (Since the car started from rest, your "u" is 0.)

    In this problem, those equations become v= 3.2t and 40= 1.6t^2. Solve the second equation for t and put that into the first equation.
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