# Vf (final velocity)

Discussion in 'Physics' started by ronn, Feb 13, 2009.

1. ### ronn Thread Starter Member

Nov 1, 2007
16
0
if i'm conducting an experiment (like letting a small toy car run from start, time it from start to the certain point that i want to know Vf(final velocity))
what formula should i use to know Vf? should i know the accelration first but how? i'm trying to use the formula
a = (Vo + Vf)/t where
a=acceleration
Vo=Inital velocity in (meters/s)
Vf=Final velocity in meters per second
t=time in seconds
not constant acceleration
but still a liitle bit confused of what to do
thanks
(sorry for my wrong formula of acceleration before)
Ron

Last edited: Feb 14, 2009
2. ### mik3 Senior Member

Feb 4, 2008
4,846
63
Will the car have a constant acceleration?

How you will measure it?

3. ### jpanhalt AAC Fanatic!

Jan 18, 2008
5,699
909
Your first equation for acceleration (i.e., a = (Vo + Vf)/2 ) just doesn't make sense. Why don't you write the units for velocity and see whether you end up with the correct units for acceleration doing it that way?

John

4. ### mik3 Senior Member

Feb 4, 2008
4,846
63
If the car has a constant acceleration then you can use:

s=0.5*a*(t^2)

to find the distance

Otherwise you need to make a circuit which will measure the speed of the car at any instant in time and integrate it as to find the distance (s).

5. ### fanta_hanu New Member

Mar 9, 2009
8
0
(Vf)2-(Vi)2 = 2*a*S

Where Vf = Final Velocity
Vi=Initial Velocity(=0,if it starts from rest)
a= acceleration
S= distance covered.

S=[(Vi)*t]+[.5*a*t2]

Where t= time of journey..

Using these you can calculate the required parameters...provided,the acceleration in uniform..

If its not uniform and a variable one,Use differential form..

a=dv/dt=d/dt(v) where v=velocity,in terms of time

Hope this would solve your problem...If you want more,do let me know...

Cheers,
hanu