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Homework Help: A task from kinematics

  1. Aug 2, 2016 #1
    1. The problem statement, all variables and given/known data
    I am stuck with this task please help me.

    1. A body is moving with constant deceleration while passing through path that contains two same parts and each one of them is 10m. The first part of the path, body passes for t1= 1s and the second part passes for t2=2.2s. Determine decelartion of the body!

    2. Relevant equations
    I assume :
    First part of the path : s1= vot1- (at12)/2
    Second part of the path : s2= vt2 - (at22) /2
    V = Vo -at1

    3. The attempt at a solution
    I tried to sum s1 + s2 because the whole path is s = s1 + s2 and then to find acceleration but this was not good because I left with initial velocity. I tried it many times but each time unsuccessfully.

  2. jcsd
  3. Aug 2, 2016 #2

    Doc Al

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    Staff: Mentor

    So far, so good.
    Use the values given for the distances and times and you'll have two equations and two unknowns. Solve!
  4. Aug 2, 2016 #3


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    Gold Member

    If you assume the same constant deceleration in both the paths It seems correct. You have two equation and two data to find ##a## and ##v_{0}##, try to solve the system ...
  5. Aug 2, 2016 #4


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    Science Advisor
    Homework Helper
    Gold Member

    That's ok, but that's going from two pieces of information to one. As Doc Al says, you need to make the use of the fact that you know the two distances separately. Since in this case the two distances are the same, one interesting avenue to try is subtracting the two equations to produce another.
    That introduces yet another unknown, the velocity at the boundary. Can you think of another equation along these lines?
  6. Aug 3, 2016 #5
    Ive found it ! Deceleration is a= 3,4 m\s2

    Thanks everyone for help :))
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