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Homework Help: 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
    Victim:
    1. Adam Able. 5'11. 160 lbs.

    Suspects:
    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.
    Xo=0
    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

    gneill

    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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