# how to calculate final velocity of car

• Sep 17th 2011, 06:49 PM
moonnightingale
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
• Sep 17th 2011, 06:53 PM
moonnightingale
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
• Sep 18th 2011, 12:38 AM
mr fantastic
Re: how to calculate final velocity of car
Quote:

Originally Posted by moonnightingale
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 \$\displaystyle 2as = v^2 - u^2\$, substitute the given data and solve for v.
• Sep 18th 2011, 03:28 AM
HallsofIvy
Re: how to calculate final velocity of car
Quote:

Originally Posted by moonnightingale
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 \$\displaystyle 40= 1.6t^2\$. Solve the second equation for t and put that into the first equation.