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Homework Help: One-Dimensional Kinematics problem

  1. Jun 23, 2005 #1
    Hi, i have some questions for the following problems.

    A car accelerate at -1.9 m/s2. Traveling at a constant velocity of 32 m/s, this car comes up behind a car traveling at a constant velocity of11 m/s.

    a) How close to the slower car can the driver of the faster car come before applying his brakes and still avoid a collision?

    b) At what time does the inevitable collision of the two cars occur?

    c) How far beyond its position at t = 0 does the slower car get before it is hit?

    so the |a1| = 1.9 m/s2
    v1 = 32 m/s
    v2 = 11 m/s.

    Since it accelerates in a negative direction then it is deccelerating at a constant rate. For every second the velocity with decrease by 1.9 until it crashes with the second car with has a constant velocity. Now I dont understand what the question is asking for part a)

    Can anyone help? thanks
  2. jcsd
  3. Jun 23, 2005 #2


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    Write the equations of motion for each car and then impose the conditions that fulfiled for the crash to happen.

  4. Jun 24, 2005 #3
    hi thanks for the reply.
    I found that the two equations for the position.

    X1 = V1t + .5 at^2
    X2 = D + V2t

    If i set these two equal, I should find the point of collision but there are two variables and they dont give me D or T. If they have given me D then the problem will be alot easier.

    On the first problem, I want to find the D but they did not provide me with a time.
  5. Jun 24, 2005 #4
    Try using the velocity equation for car 1 to find t.
  6. Jun 25, 2005 #5
    Better yet, use concept of relative velocity and relative acceleration. Set the final relative position at 0 and solve for initial position.
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