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

Another Mythbusters experiment

  1. Nov 12, 2007 #1
    I'm just a high school physics student, and this is my first physics class. Anyways, I was watching Mythbusters a few days ago and saw the myth that a car could turn 90 degrees @ high speeds if a grappling hook was shot out at a structure at the corner of a turn (see diagram below). I've never dealt with centripetal forces before and was just wondering how you would create a force diagram for an object with centripetal forces.
    http://img111.imageshack.us/img111/4167/carscenarioks7.jpg [Broken]
    Here's my take on it, but I'm just blindly guessing here:
    http://img405.imageshack.us/img405/7481/cardiagrasmk3.jpg [Broken]
    Note that the car is already caught in the circular motion when position 2 is drawn. Also, forgive my messy handwriting and drawings :)
    Last edited by a moderator: May 3, 2017
  2. jcsd
  3. Nov 12, 2007 #2
    well i think you got the fpr and f on the car by engine wrong cause when the car is turned the engine of the car gives the force along the direction where the car is pointing (provided the wheels of the cars are not turned) and also the friction on th motion ofthe car depends on the direction the car is moving so since the car is is turning the direction of friction force also changes..... also i would like to point out that the f nx will be caused because of the change of momentum of tha car as it turns.... hope this helps :shy:
  4. Nov 12, 2007 #3
    Besides the the centripetal force question, there is the very great possibility that a human in that car will not survive the fairly high da/dt at the tangent point of the curve. Likely, cervical injury or "brain spin" would be fatal, depending on the speed and radius of curvature.
  5. Nov 12, 2007 #4
    Using the equation :

    a = (v^2)/r

    Lets say the car is travelling at 70 mph and the radius of the turn is 2m.

    a = (31.11^2)/2 = 484 m/s^2

    Or 50g, so yea its unlikely you would survive that lol
  6. Nov 12, 2007 #5
    Less likely that the signpost will survive.
  7. Nov 12, 2007 #6
    how did you make those images
    Last edited by a moderator: May 3, 2017
  8. Nov 12, 2007 #7
    The tension in the cable is going to be pretty high though, say you had a fairly normal 1.5 ton saloon (think thats probably about right), thats a tension of something like 726kN so if your cable is made out of something like mild steel it'll need to be fairly thick to deal with it and firing a cable like that at the extremely strong signpost in the first place is going to be pretty difficult.
  9. Nov 12, 2007 #8
    I did not give sufficient information about da/dt injury. If the reader wants, there is a wealth of information to be found in most biomechanics texts, or by Googling Contrecoup injury or whiplash.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook