Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Using kinematics, projectiles, conservation of momentum to find pre-collision speeds

  1. Oct 17, 2011 #1
    1. The problem statement, all variables and given/known data
    There was a snowmobile accident on Ramsey Lake in Northern Ontario. A police officer arrives at the scene of the collision of the two snowmobiles to find both drivers unconscious. When the two vehicles collided, their skis became entangled and the two snowmobiles remained locked together as they skidded to a stop. One driver was thrown clear from the mishap, but the other driver remained in the driver's seat. The posted speed limit for snowmobiles in the cottage area is 60km/h. The information the police officer obtained from eye witnesses accounts the collision scene measurement are provided. One witness described how driver A was thrown horizontally at a constant speed from his seat (0.5m above the snow surface) to his final resting position.

    mass of driver A= 80kg
    mass of driver B= 90kg
    mass of vehicle A= 270kg
    mass of vehicle B= 310kg
    direction of vehicle A before collision= [E]
    direction of vehicle B before collision= [E30N]
    direction of entangled vehicles A and B after collision= [E15N]
    length of final skid= 18m
    displacement of driver A from point of impact= 8m
    time from impact to end of ski= 2.5s

    Required: Find the velocities of both snowmobiles prior to the accident

    Diagram: http://i55.tinypic.com/29to5x.jpg

    2. Relevant equations
    d = vt - (1/2)at^2
    Total original momentum = Total final momentum

    3. The attempt at a solution
    Used knowledge of kinematics and projectiles to find velocity of passenger A after the accident. V = 25m/s [E45N]

    Used v= d/t to find velocity of the snowmobiles after the accident
    d = v/t = 18/2.5 = 7.2m/s[E15N]

    Broke down both velocities into x and y components:

    x velocity of passenger A = (cos45)(25) = 17.7m/s [E]
    y velocity of passenger A = (sin45)(25) = 17.7m/s [N]

    x velocity of snowmobiles = (cos15)(7.2) = 7m/s [E]
    y velocity of snowmobiles = (sin15)(7.2) = 1.8m/s [N]

    At this point I'm completely stumped; i have no idea what to do next. Any help and/or hints would be greatly appreciated. Also, first post on this forum! :smile:
    Last edited: Oct 17, 2011
  2. jcsd
  3. Oct 17, 2011 #2
    Re: Using kinematics, projectiles, conservation of momentum to find pre-collision spe

    Sorry for double post, I realised i left out some important information the first time I posted it. Updated with additional given information.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook