# Homework Help: Acceleration problem

1. Feb 1, 2008

### sprinter08

1. The problem statement, all variables and given/known data

A sports car accelerates from rest to 100km/hr in 6.2s. What is it's acceleration in m/s^2?

2. Relevant equations

3. The attempt at a solution
I converted the 100 km/hr to m/s and got 16.7 m/s. I think that the formula that I am supposed to use is Vf-Vo/t. I don't know what to do next or if even what I did is correct.

2. Feb 1, 2008

### dlgoff

100 km/hr=(100x1000)meter/60min=(100x1000)meter/(60x60)sec=27.8meter/sec.

Now look at the units for acceleration. This should tell you what you must do with velocity(m/s) to get m/s^2.

3. Feb 1, 2008

### Newton1Law

100 kM/hr = 27.78 m/s not 16.7 m/s. Look in your book. You should find a reference equation that looks something like v=at+vo. Since you know v0=o at time=0 the equation becomes simple. Now solve for acceleration since you have been given both the time and final velocity.

Hope this helps.

4. Feb 1, 2008

### rsala

since 100km/h = 27.8 m/s

use v^2 = V0^2 + 2a(y-y0)

27.8^2 = 0 + 2a(y) ; 2 unknowns
/////(27.8^2) / 2a = y

then use y = y0+v0T+.5aT^2
plug in with the Y you solved for in the other equation.
772.84 / 2a = 0 + 0T + .5aT^2
remember t = 6.2
solve for a; a = 4.48 m/s^2

check my math, i dont know

Last edited: Feb 1, 2008
5. Feb 1, 2008

### dlgoff

You are making it too complicated. You have one equation with one unknown: v=at+vo

6. Feb 3, 2008

### sprinter08

I'm not sure if I exactly understand. I understand a little more than I did before. It is hard for me because my class does not use a book and we have one practice problem as our notes.

Last edited: Feb 3, 2008
7. Feb 3, 2008

### dlgoff

This (Vf-Vo/t) is what you showed in your first post for finding the acceleration a. And as Newton1Law wrote, "Since you know v0=o at time=0..." then a=Vf/t. That's all there is to it.

8. Feb 3, 2008

### sprinter08

Thank you. That makes sense to me now.