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Kinematics problem -- A lift ascends from rest with uniform acceleration

  1. Jan 23, 2015 #1
    1. The problem statement, all variables and given/known data

    A lift ascends from rest with uniform acceleration of 4m/s², then it moves with uniform velocity and finally comes to rest with uniform retardation of 4m/s². If the total distance covered during ascending by the lift is 28m and the total time for ascending 8s respectively, then find the time for which the lift moves with uniform velocity. Also find its uniform velocity.
    2. Relevant equations


    3. The attempt at a solution
    I am trying to find the time for acceleration, retardation and uniform velocity separately by using equations of motion....but somehow I am not being able to solve it....the information looks inappropriate.
    (The answer given is 4m/s)
     
  2. jcsd
  3. Jan 23, 2015 #2

    BiGyElLoWhAt

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    You need to set up a system of equations. You have the time and acceleration.
     
  4. Jan 23, 2015 #3

    SteamKing

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    Well, you should show your best attempt at solution.

    Hint: since the elevator starts and stops with the same magnitude of acceleration, namely 4 m/s2, it would be reasonable to assume that the amount of time spent accelerating to the unknown constant velocity is the same amount of time required to come to a stop. You should be able to write some kinematics equations knowing the total time and distance to solve for the unknown constant velocity.
     
  5. Jan 23, 2015 #4
    Please solve it
     
  6. Jan 23, 2015 #5

    SteamKing

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    Sorry, that's your job. The Rules of PF prohibit members from providing full solutions to HW problems in the HW forums.

    We've given you some hints on how to find a solution, so take the next step and show us what you can do with this problem.
     
  7. Jan 23, 2015 #6

    BiGyElLoWhAt

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    Ok, I solved it, now you solve it.
     
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