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Kinematics - Find velocity of the car

  1. Sep 6, 2007 #1
    1. The problem statement, all variables and given/known data

    Find velocity of car A when car A and car B meet
    Find the distance from where car B started to where car B meets car A
    Find the time it takes car A to reach car B

    initial velocity of car A is 0
    initial velocity of car B is 26.67 m/s
    at t=5, acceleration of car B = -1/6 * acceleration of car A
    velocity of car A=velocity of car B when they meet

    2. Relevant equations


    X_A(t)=X_A(0) + V_A(0)*t + .5*a_A*t^2
    V_B=V_B(0) + a_B*t
    3. The attempt at a solution

    distance of car A equation becomes this.....90=.5*a_A*t^2
    velocity of car B becomes this....V_B=-26.67 - 1/6*a_A*t

    I tried solving X_A equation for a_A and using it in V_B but no luck, I spent 3 days trying every which way I could think of to find the answer.

    The answers in the back of the book are
    Acceleration of car A=3.59 m/s^2
    time=7.08 s
    distance car B travels=188 m
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     

    Attached Files:

  2. jcsd
  3. Sep 6, 2007 #2

    Gokul43201

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    Gold Member

    #1. Write down the time taken for A, using the least number of unknowns (use as much of the given data as possible).

    #2. Write down the final speed of A in a similar manner. This is also the final speed of B.

    #3. Independently, write down an expression for the final speed of B in terms of the time taken (B takes the same time as A; see #1).

    #4. Use the relationship between the two accelerations and set the two expressions for the final speed of B equal to each other.
     
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