# Finding car speed

## Homework Statement

A race car starting from rest accelerates uniformly at a rate of $4.90m/s^{2}$ . What is the car's speed after it has traveled 200m?

## Homework Equations

Δv = $\frac{Change in position}{change in time}$

## The Attempt at a Solution

v=$\sqrt{980m^2/s^2}$

=31.3m/s

Related Introductory Physics Homework Help News on Phys.org
SammyS
Staff Emeritus
Homework Helper
Gold Member

## Homework Statement

A race car starting from rest accelerates uniformly at a rate of $4.90m/s^{2}$ . What is the car's speed after it has traveled 200m?

## Homework Equations

Δv = $\frac{Change in position}{change in time}$

## The Attempt at a Solution

v=$\sqrt{980m^2/s^2}$

=31.3m/s

How did you get $v=\sqrt{980m^2/s^2}\,?$

gneill
Mentor
What kinematic formula are you using? It looks like you've missed out a constant.

How did you get $v=\sqrt{980m^2/s^2}\,?$
What kinematic formula are you using? It looks like you've missed out a constant.
Well I'm required to find the speed after 200 meters, but I was never given any time.

So I assume... Which is not a good thing to do, multiplying the acceleration * the distanced travel would give me the speed.

But I really can't remember the actual equation.

gneill
Mentor
Well I'm required to find the speed after 200 meters, but I was never given any time.

So I assume... Which is not a good thing to do, multiplying the acceleration * the distanced travel would give me the speed.

But I really can't remember the actual equation.
If you can't remember you should check your notes or text book! Your formula is close to being a valid kinematic expression,... but it's missing a constant. Do you have a list of the common kinematic expressions?

If you can't remember you should check your notes or text book! Your formula is close to being a valid kinematic expression,... but it's missing a constant. Do you have a list of the common kinematic expressions?
I have the text book, and I did have an example sheet but my friend borrowed to check her work. I found this expression which seems to satisfy my problem, v2 = vo2 + 2a(X - Xo)

Therefore V2= 0m/s + 2(4.90m/s^2)(200m)

v2= 9.8m/s^2(200m)
v2= 1960m^2/s^2
v=$\sqrt{1960m^2/s^2}$
v= 44.3m/s

gneill
Mentor
I have the text book, and I did have an example sheet but my friend borrowed to check her work. I found this expression which seems to satisfy my problem, v2 = vo2 + 2a(X - Xo)

Therefore V2= 0m/s + 2(4.90m/s^2)(200m)

v2= 9.8m/s^2(200m)
v2= 1960m^2/s^2
v=$\sqrt{1960m^2/s^2}$
v= 44.3m/s
That looks better