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Homework Help: Discrepancy with Toricellis equation in a 2D kinematics prob

  1. Dec 30, 2015 #1
    1. The problem statement, all variables and given/known data
    A stone is thrown from a height 2.1m with an angle of 45 degrees. It fell to the ground 42 m from the throwing position, measured horizontally. Initial velocity is 19,81 m/s, flight time is 3s what is the maximum height?

    2. Relevant equations
    All 2D kinematics equations.

    3. The attempt at a solution
    I plugged in the variables into the equation y(t), and equated Vfin=0, for the maximum height and obtained the correct result which should be 10m from the starting position and 12,1m from the ground. But when I tried to solve the problem using equation Vfin^2=V0^2+2gΔy I obtain 20m which is not correct. Why is it not correct?
  2. jcsd
  3. Dec 30, 2015 #2


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    You will need to show more of your work in order for us to find the error. Are the velocities in this equation supposed to be y-components of velocity?
  4. Dec 30, 2015 #3
    Thank you very much! It was my careless mistake. I didn't use y-components of velocity. Thank you! Turns out to be consistent. Thanks again.
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