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Homework Help: Finding the fianl Velocity

  1. Mar 11, 2010 #1
    1. The problem statement, all variables and given/known data
    The model is a car with weights dropping from certain height and propels the car forwards. (Some GPE converted to KE knowledge involved.) And the question is to find a theoretic maximum velocity (final velocity) as the mass of car/weight and the height of weights are constant. All the frictions are not taking in consideration. We know the distance(s) and the time (t), also the M (mass of weights) and the H(height of weights).

    2. Relevant equations
    What I did is to measure the running time of car and the distance the car traveled within this time. Therefore, the work has done is completely equal to the kinetic energy. W=KE=GPE=mgh. (Due to the formula W=Fd, the force can be calculated. Then F=ma, acceleration of car has worked out. Finally the V, by Vt=V0+at, is calculated.

    3. The attempt at a solution
    My question is that is this the easiest way to solve it? Is there any other method that can work without thinking so many procedures?
  2. jcsd
  3. Mar 11, 2010 #2


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    Homework Helper

    Welcome to PF!

    Hi wermichiel! Welcome to PF!

    Your formula W = Fd (for the work done) doesn't really work in this case (what is d?).

    As you say, KE = GPE= mgh,

    so just use KE = 1/2 mv2. :wink:
  4. Mar 11, 2010 #3
    thanks for answering.
    but what i trying to do is comparing the actual and theoretical final velocity
    as I cannot measure the actual final velocity in the experiment, only average velocity can be worked out by Va= S/t =.=
    however the KE=1/2mv^2 is dealing with the final velocity
    this is where I am struggling
    W=fd, f=force d=distance, w= work
  5. Mar 11, 2010 #4
    a = 2(s - ut)/t2
    ah!! a formula is applied to this condition!!!
    calculating the A by this way can avoid the calculation of work
    then use V=U+at , there is the V!
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