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Homework Help: A level question kinematics

  1. Mar 15, 2010 #1
    1. The problem statement, all variables and given/known data
    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.


    2. Relevant equations

    usual suvat

    3. The attempt at a solution
     
  2. jcsd
  3. Mar 15, 2010 #2
    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?
     
  4. Mar 15, 2010 #3
    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
     
  5. Mar 15, 2010 #4
    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.
     
  6. Mar 15, 2010 #5
    Yip, that done it...lol thanks alot 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
     
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