Maximizing Velocity in Uniformly Accelerated Motion

[jh128273]

Homework Statement

a car takes 3 mins to travel between 2 sets of traffic lights which are 1800m apart, its velocity at each set of lights is 0ms-1

If the car accelerated uniformly for 30 secs and then maintained a constant velocity for the next 2 mins before retarding uniformly, calculate the the maxumum uniform velocity reached.

Homework Equations

usual suvat

The Attempt at a Solution

 

[Stonebridge]

Welcome to Physics Forums.
It's probably best done drawing a velocity time graph and using the fact that the area under the graph is the distance travelled.
Have you tried that?

 

[jh128273]

Thanks for the quick reply.

Yes I have looked at that but as I didnt have a velocity it seemed useless.

I think I'm struggling as there is only 2 components to use i.e. time and total distance.

I'll keep trying :)

cheers

 

[Stonebridge]

The shape of the graph is a trapezium. If you know the formula for its area you have all you need to find the "height" of it. (Height= maximum velocity of car)
If you don't know the formula, treat the graph as 2 triangles and a rectangle and write down the area of each of those 3 shapes in term of the "height" of the graph.
Triangle area is half base times height. Rectangle is length times height.

 

[jh128273]

Yip, that done it...lol thanks a lot for your help, it has cheers me up after a freak out earlier. I think I've been looking into further than was needed.

Thanks again,

Jeff