# Finding the fianl Velocity

1. Mar 11, 2010

### wermichiel

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. Mar 11, 2010

### tiny-tim

Welcome to PF!

Hi wermichiel! Welcome to PF!
Yes!

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.

3. Mar 11, 2010

### wermichiel

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

4. Mar 11, 2010

### wermichiel

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!