Simple kinematics problem: avg. acceleration if a car's going 12 m/s and accel

1. Sep 28, 2009

therest

A basic kinematics problem that I just can't get for some reason. I'm having trouble visualizing the graph.

1. The problem statement, all variables and given/known data
What's the average acceleration if a car's going 12 m/s constant speed, then accelerates for 12 seconds at 1.7 m/s^2 acceleration?
Variables: none?

2. Relevant equations
? I do not know. At all.

3. The attempt at a solution
I had graphed speed over time with the function as a horizontal line until it reached the origin, where it gained a slope of 1.7 because of the acceleration. I don't know if I'm visualizing the increase in speed correctly or if it would become an exponential curve. If this was the result, I don't know how I would then find average speed--total distance over time. Would I need to know calculus to figure this out? So this is where I'm stuck.

Last edited: Sep 28, 2009
2. Sep 28, 2009

Delphi51

Missing information - it doesn't say how long it is going at constant speed.
You could use v = vi + at to find the final velocity.
The average acceleration would be a = (change in velocity)/time
where "time" would be the total of the constant speed time and the 12 seconds of acceleration.

3. Sep 29, 2009

therest

Whoops! Yeah, I forgot to specify that the 12 s was the entire period... the time when it was going 12 m/s was not included in calculations except as a starting value, i.e. v(0).

I'm sorry, I did ending up figuring this out. It was just averaging 12 m/s with the speed after 12 s with acceleration, which was 32.4 m/sec - 1.7 m/s^2 times 12 seconds and plus 12 m/s initial speed - to get 22.2 m/sec.

Oh, and I put average acceleration instead of average speed. Well. I'm sorry, I was not being nice to you. :(