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Kinematics rock thrown up in air

  1. Feb 6, 2009 #1
    kinematics .... rock thrown up in air

    1. The problem statement, all variables and given/known data


    If a rock is thrown upward on the planet Mars with a velocity of 22 m/s, its height (in meters) after t seconds is given by H = 22t - 1.86t^2.
    Find the velocity of the rock when t = a.
    When will the rock hit the surface?
    With what velocity will the rock hit the surface?

    2. Relevant equations
    v=u+at



    3. The attempt at a solution
    i found the ans for first two ques but i am not able to solve the third one.

    velocity at t=a is 22-3.72a
    rock will hit the surface at t=11.83s

    pls help me with the third one...
     
  2. jcsd
  3. Feb 6, 2009 #2

    LowlyPion

    User Avatar
    Homework Helper

    Re: kinematics .... rock thrown up in air

    Welcome to PF.

    Gravity is a conservative field. So at the same height going up ...

    |Vinitial| = |Vfinal|

    ... going down.

    Or you could do it the long way and evaluate

    V = Vinitial - a*t

    Using the total time of flight.
     
  4. Feb 6, 2009 #3
    Re: kinematics .... rock thrown up in air

    thanks i got that!!
     
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