# Thread: can't figure out acceleration formula

1. ## can't figure out acceleration formula

Hi;
A car accelerates from rest at a constant rate of 2m/s^2. For 5 seconds, What is the speed of the car after 5 seconds?

The part I'm finding difficult is the formula part 2m/s^2.

ie for the first second its speed is 2/1^2 = 2 metres.

for the second second I get 2/2^2 = 2/4 = 0.5, How would I get 4 metres?

Thanks.

2. ## Re: can't figure out acceleration formula

First, you are asked to find the car's speed after 5 seconds and speed is measured in "metres per second", m/s, not "metres".

Second the "m" and "s" in "m/s^2" are not "variables" to be substituted for, they are just telling you what units are being used. Acceleration is defined as "change in speed divided by change in time" (so that speed, m/s, is divided by time, s, giving m/s^2) so to go the other way, from acceleration to speed, reverse that and multiply by the change in time. At constant acceleration, 2 m/s^2, for 5 seconds, the cars speed will increase by (2 m/s^2)(5 s)= 10 m/s.

3. ## Re: can't figure out acceleration formula

Originally Posted by HallsofIvy
measured in "metres per second", m/s, not "metres".
metres is the perfectly legitimate British spelling of the word.

4. ## Re: can't figure out acceleration formula

Yes, I agree, and I used the spelling "metres" in my response because that was what anthonye used. My point was that he was incorrect to say "ie for the first second its speed is 2/1^2 = 2 metres" rather than "metres per second".

5. ## Re: can't figure out acceleration formula

Originally Posted by HallsofIvy
Yes, I agree, and I used the spelling "metres" in my response because that was what anthonye used. My point was that he was incorrect to say "ie for the first second its speed is 2/1^2 = 2 metres" rather than "metres per second".
Ah, yes, you are correct. My apologies.