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Murder Mystery Solution using Kinematic Equations

  1. Sep 25, 2011 #1
    I'm new to this site, so let me know if I'm doing anything wrong.

    1. The problem statement, all variables and given/known data
    I have attached the original problem in a PDF file. I have to read a murder mystery story and pull information from it to plug into kinematic equations and find out who commited the murder.

    Important information that I have pulled out of the story:
    --No air resistance
    --Each room is has a 14ft high ceiling with 2 feet between each floor.
    --Bloodstains are 18ft from the entrance to the building
    1. Adam Able. 5'11. 160 lbs.

    1. Adrianna Myers (Room 356)
    2. Steven Caine (Room 852)
    3. Mark Johnson (Room 1956)
    4. Stanley Michaels (Room 2754)

    2. Relevant equations
    Kinematic Equations:
    1x. V=Vo+at
    2x. X=Xo+1/2(V+Vo)t
    3x. X=Xo+Vot+1/2at^2
    4x. V^2=Vo^2+2a(X-Xo)

    1y. Y=Vo+at
    2y. Y=Yo+1/2(V+Vo)t
    3y. Y=Yo+Vot+1/2at^2
    4y. V^2=Vo^2+2a(Y-Yo)

    Xo & Yo = Initial Position
    X & Y = Final Position
    Vo = Initial Velocity
    V = Final Velocity
    A = Acceleration
    T = time

    3. The attempt at a solution
    Knowing that each floor is 16ft total, I use the person's room number to find out high up the are. I know that in the end I need to figure out how high up Adam fell from and compare that to the suspects rooms to know who killed him. Note: I've also converted everything to meters

    The first thing I did was solve for time using the x-axis equations.
    X= 5.4864 m (18ft where bloodstains were)
    Vo = 0 m/s
    V = 2 m/s (You'll notice in the attached file that our teacher gives a hint stating that if we were in lab and pushed our partner hard, we'd find that they'd have a speed of 2 m/s)
    a = ?
    t = Find!
    I plugged all of this into Equation 2x and got 5.864 seconds. (I believe this is wrong after going further, I'm just explaining what I did.

    The second thing I did was plugged in the time to find out Yo.
    Yo = Find!
    Y = 0 m
    Vo = 0m/s
    V = ?
    a = -9.81 m/s (Gravity)
    t = 5.4864 s
    I plugged this into Equation 3y and got 25.24 m. This is seeming way off.

    I know this is long. This is a take-home problem for my exam tomorrow. I'm not asking anyone for answers. I just need help going in the right direction. This is my first physics class ever and its turning out to be way harder than I expected and I have no friends takign classes like mine.
    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 25, 2011 #2


    User Avatar

    Staff: Mentor

    For the horizontal motion, Adam's initial velocity will be about 2m/s and there will be no acceleration in the horizontal direction after he's shoved. It looks like your equation 3x would be the better choice, setting a to zero.
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