# Acceleration confussion

• Oct 20th 2011, 01:52 PM
vaironxxrd
Acceleration confussion
I have solved an example problem given in my book, but I don't understand why are the second being squared.

$\frac{0 m/s - 30m/s}{3.0s}$ = -10m/s^2

Is it looking like this at some point $\frac{-30 m^2/s^2}{3.0s}$

And if so why are the seconds not canceling?
• Oct 20th 2011, 02:03 PM
skeeter
Re: Acceleration confussion
remember how to divide fractions?

$\frac{\frac{m}{s}}{s} = \frac{\frac{m}{s}}{\frac{s}{1}} = \frac{m}{s} \cdot \frac{1}{s} = \frac{m}{s^2}$

you need to understand that acceleration is the change in velocity per unit time ... (meters per second) per second = $\frac{m}{s^2}$
• Oct 20th 2011, 04:55 PM
vaironxxrd
Re: Acceleration confussion
Quote:

Originally Posted by skeeter
remember how to divide fractions?

$\frac{\frac{m}{s}}{s} = \frac{\frac{m}{s}}{\frac{s}{1}} = \frac{m}{s} \cdot \frac{1}{s} = \frac{m}{s^2}$

you need to understand that acceleration is the change in velocity per unit time ... (meters per second) per second = $\frac{m}{s^2}$

So if I was given the acceleration of let's say a car,

Acceleration = $5m/s^2$

And I would like to know how long would it take a car traveling at 20m/s To reach 30m/s

Would I just say $\frac{10m/s}{5m/s^2}$

= 2s?
• Oct 20th 2011, 05:00 PM
skeeter
Re: Acceleration confussion
yes, since ...

$a = \frac{\Delta v}{\Delta t}$

then ...

$\Delta t = \frac{\Delta v}{a}$