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Settle an argument please

  1. Sep 12, 2006 #1
    Settle an argument please !!

    Look at the picture. The van is travelling forwards at 100mph.

    A motorcycle is ridden forwards out the van, off a ramp at 20mph.

    1) what direction will the bike front wheel be travelling as it leaves the ramp.
    2) What direction will the whole bike be travelling as it rolls of the ramp
    3) What direction will the bike be travelling at when both wheels exit the ramp.

    I believe the front wheel will hit the tarmac, skid to a stop then start travelling in the same direction as the van wheels.

    As the rear wheel exits the van, it will also skid to a halt and also start turning at at the same direction as the van wheels. The bike then will be travelling in reverse, in the same direction as the van until it comes to a stop, then will start travelling in the opposite as the van under its own power.

    I think you would have to leave the ramp at more than 100mph to make the bike be travel immediatly in the opposite direction as the van.

    Others think the bike will travel in the opposite direction as the van as soon as it exits the van if the bike is travelling at 20mph.

    please ignore the potential to crash etc !!

    http://img214.imageshack.us/img214/7961/vanju9.jpg [Broken]
    Last edited by a moderator: May 2, 2017
  2. jcsd
  3. Sep 12, 2006 #2


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    Staff: Mentor

    Depends. Are the bike's wheels free to change speed (are they freewheeling at the moment of contact with the road)? Or is just the front wheel free to change speed (with a chirp), but the rear wheel is hard driven at 20mph by an engine?
  4. Sep 12, 2006 #3


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    Gold Member

    Reminds me of KITT coming out of the service truck on Knight Rider. :biggrin: I always wondered how many tires they burned through on that show.
  5. Sep 12, 2006 #4
    when you say 20mph, do you mean with respect to the van, or with respect to the ground?
  6. Sep 12, 2006 #5


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    Homework Helper

    The bike exits the van at 80mph going backwards, in the same direction as the van, a crash will soon follow.
  7. Sep 13, 2006 #6


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    Lets assume the bike is free wheeling. The initial velocity of the bike will be 80 mph in the direction the truck is traveling. The tires will at first skid, then reverse their direction of rotation from 20 mph counter clockwise to clockwise in the direction of travel. Losses will be due to friction and the energy required to accelerate the wheel mass in the opposite direction until they catch up with the road surface. I would guess the bike would end up traveling around 70 mph in the direction of the truck. At 100 mph, the bike would basically come to a dead stop
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