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Thread: Circular Motion Question

  1. #1 Circular Motion Question 
    Forum Bachelors Degree x(x-y)'s Avatar
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    So, this was one of a few questions I got given in a physics lesson (A2 level, if you're wondering) today- and it seems that it doesn't give you enough information to answer:

    "If the combined mass of Dan and his bicycle is 1000kg [rather large, I know!] calculate the centripetal force if his turning circle has a radius of 3m".

    So, as far as I can see, this question is unanswerable as it cannot be answered directly using



    or by using a value for a time (as none was given), and working out linear velocity from there using



    Any suggestions? Or is it unanswerable?


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  3. #2  
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    You need to know the rotational speed. If this is one of those multi-part exercises, maybe it was given in another part of the problem.


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  4. #3  
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    Quote Originally Posted by Harold14370
    You need to know the rotational speed. If this is one of those multi-part exercises, maybe it was given in another part of the problem.
    You are given the turning radius, so the linear speed would suffice.

    Since this dude plus the bycycle has a mass of 1000kg and the bike probably weighs only 25 kg or so, it unlikely that v is much over 0.
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  5. #4  
    Reptile Dysfunction drowsy turtle's Avatar
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    An interesting route to persue would be whether or not a typical bicycle could support a whole ton of passenger. I suspect not.
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  6. #5  
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    Quote Originally Posted by drowsy turtle
    An interesting route to persue would be whether or not a typical bicycle could support a whole ton of passenger. I suspect not.
    The frame should handle a static load like that handily. The tires would be a problem (even at 100 psi you would need 22 in^2 of contact area with the road).

    All bets are off if he hits a bump..

    A really big seat would be required.

    I have no idea how such a giant would get on the bike in the first place.
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  7. #6  
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    I do think it's rather hilarious the mass of him and the bike!

    And, no, by the way, this isn't a multipart question- I should've stated that in the original post, sorry.
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  8. #7  
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    Quote Originally Posted by DrRocket
    Quote Originally Posted by drowsy turtle
    An interesting route to persue would be whether or not a typical bicycle could support a whole ton of passenger. I suspect not.
    The frame should handle a static load like that handily. The tires would be a problem (even at 100 psi you would need 22 in^2 of contact area with the road).

    All bets are off if he hits a bump..

    A really big seat would be required.

    I have no idea how such a giant would get on the bike in the first place.
    Perhaps the person isn't a giant, but is just rather dense so to speak- obviously not your typical human!
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  9. #8  
    Samurai of Logic Falconer360's Avatar
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    Quote Originally Posted by x(x-y)
    Perhaps the person isn't a giant, but is just rather dense so to speak- obviously not your typical human!
    I do know some people with dense enough skulls that might fit the bill. lol
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  10. #9  
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    Quote Originally Posted by Falconer360
    Quote Originally Posted by x(x-y)
    Perhaps the person isn't a giant, but is just rather dense so to speak- obviously not your typical human!
    I do know some people with dense enough skulls that might fit the bill. lol
    Hehe, that is true- I wouldn't rule some (well, all) creationists out of that category.
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  11. #10  
    Samurai of Logic Falconer360's Avatar
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    Too true! x(x-y) rofl
    "For every moment of triumph, for every instance of beauty, many souls must be trampled." Hunter S Thompson

    "It is easy to kill someone with a slash of a sword. It is hard to be impossible for others to cut down"
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    "Only a warrior chooses pacifism; others are condemned to it."
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  12. #11  
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    The question should not require a velocity. A certain amount of force must be applied to cause a certain amount of deviation, regardless of whether this much force is applied in one go or over a long period of time.

    Edit-to-add: Unless I'm missing something. I have had some bad news and some wine.
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  13. #12  
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    Quote Originally Posted by PhysBang
    The question should not require a velocity. A certain amount of force must be applied to cause a certain amount of deviation, regardless of whether this much force is applied in one go or over a long period of time.

    Edit-to-add: Unless I'm missing something. I have had some bad news and some wine.
    It is a straight centrepital force/acceleration problem. You need the angular velocity, which, given the turning radius, means knowing the linear velocity.

    Sorry about the bad news. I hope it was good wine.
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