Advertise on Bikeforums.net



User Tag List

Page 1 of 2 12 LastLast
Results 1 to 25 of 26
  1. #1
    '05 NUEser EJ123's Avatar
    Join Date
    Aug 2005
    Posts
    3,374
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)

    What equations do I need-homework help

    It's actually a study review he gave us for finals next week.

    1. Tarzan swings on a 30.m vine initially inclinded at a 37º angle with the vertical. What is his speed at the bottom of the swing if he:
    a. starts from rest
    b. pushes off with a speed of 4m/s
    (I dont have his mass, and I have no idea what to do with the 37º)


    2. A window washer is on one of those scaffolds with a rope on each end. The scaffold=205N and is 3m long.

    What is the force each rope exerts when a 675N worker stands 1m from one end?


    Thanks for any help. (remember I just need equations...book seems to not want to say)

  2. #2
    Senior Member
    Join Date
    Nov 2006
    Location
    Charlotte, North Carolina, USA
    My Bikes
    '71 Raleigh Sports, '84 Schwinn LeTour on the trainer (and available for hill repeats), '06 Scott CR1 SL (Ksyrium SL), and a yet-to-be-determined TT bike.
    Posts
    1,643
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    No. You need understanding of the problems. Then you'll understand how to formulate the solutions mathematically.

    Start with problem one: Can you first define in words the concepts of kinetic energy and potential energy?

  3. #3
    Senior Member
    Join Date
    Mar 2004
    Posts
    5,361
    Mentioned
    2 Post(s)
    Tagged
    0 Thread(s)
    with #1 mass wont matter, the acceleration is constant from gravity mitigated by the arc of the pendulum formed, thats more than enough of a hint

    the second one doesnt deserve any hints, just draw the picture of it and fill in what you know and what your looking for.........

  4. #4
    Crawlin' up, flyin' down bikingshearer's Avatar
    Join Date
    Jan 2006
    Location
    Democratic Peoples' Republic of Berkeley
    My Bikes
    1967 Paramount, 1982-ish Ron Cooper,1986 De Rosa Professional, 1978 Eisentraut "A," 1961 BianchiCompetizione, 1994 Trek 520, 199? Burley Bossa Nova
    Posts
    2,988
    Mentioned
    1 Post(s)
    Tagged
    0 Thread(s)
    I don't know about the math equations, but I know the lawyer equations. In both cases, fee for representing plaintiff = 33% of recovery up to mediation, 40% thereafter. Fee for representing defendant = $300+/hr.
    "I'm in shape -- round is a shape." Andy Rooney

  5. #5
    '05 NUEser EJ123's Avatar
    Join Date
    Aug 2005
    Posts
    3,374
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Ohh the pendulum jumbo, that's what I was needing to think of. Thanks pedex.

  6. #6
    Senior Member
    Join Date
    Sep 2004
    Location
    Toronto
    My Bikes
    '05 Bianchi Eros; '06 Bianchi Pista
    Posts
    490
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by bikingshearer
    I don't know about the math equations, but I know the lawyer equations. In both cases, fee for representing plaintiff = 33% of recovery up to mediation, 40% thereafter. Fee for representing defendant = $300+/hr.

  7. #7
    SERENITY NOW!!! jyossarian's Avatar
    Join Date
    Aug 2005
    Location
    In the 212
    My Bikes
    Haro Vector, IRO Rob Roy, Bianchi Veloce
    Posts
    8,757
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    In my day, we didn't have equations. We didn't even have math. We just swung from trees and didn't worry about how fast we were going.
    HHCMF - Take pride in your ability to amaze lesser mortals! - MikeR



    We demand rigidly defined areas of doubt and uncertainty!

  8. #8
    Fourth Degree Legend junkyard's Avatar
    Join Date
    Jun 2005
    Location
    American Gardens Building
    My Bikes
    2005 Kona Cinder Cone & 2010 Cannondale SuperSix
    Posts
    3,826
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    tarzan is not real, therefore the question is irrelevant
    Quote Originally Posted by dminor View Post
    The caveat with a strap-on, of course, is you will have to get creative with a couple of lock cables and an anchor point

  9. #9
    Displaced Southerner polara426sh's Avatar
    Join Date
    Apr 2006
    Location
    Webster, NY
    My Bikes
    1967 Peugeot UO-8, 1984 Torpado Beta, 1985 Trek 300, 1989 Dave Moulton Fuso FRX, '90s Hardrock x2, '90s Norco Pinnacle, Focus MB-350 IRO SSFGGB
    Posts
    254
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)

  10. #10
    riding once again jschen's Avatar
    Join Date
    Oct 2005
    Location
    San Diego, CA
    My Bikes
    '06 Cervelo R3, '05 Specialized Allez
    Posts
    7,360
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by EJ123
    Ohh the pendulum jumbo, that's what I was needing to think of.
    Oh dear... where's our new physics expert, PC2? He should be able to clarify things for you. In the meantime...

    Where to start? Umm... why don't you draw a force diagram and scan it in for us, with every relevant piece of info clearly labeled? Seriously, this needs to ALWAYS be step one. And VegaVixen is right. You're not lacking equations. You're lacking understanding.

    If you want one equation, here it is: F = ma
    If you notice this notice then you will notice that this notice is not worth noticing.

  11. #11
    Grand Vizier
    Join Date
    Feb 2006
    Posts
    21
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Here's what you need for #1:

    (potential energy from the starting point to the bottom of the arc)
    PLUS
    (added kinetic energy when he pushes off (assuming he pushes tangential to the arc (and downward)))
    EQUALs
    (kinetic energy at the bottom of the arc (assuming negligible loss of energy due to friction and wind resistance))


    Here's what you need for #2:
    All translational forces cancel out, and all rotational forces cancel out (assuming the scaffold is not accelerating either translationally or rotationally).

  12. #12
    The quieter you become... Falkon's Avatar
    Join Date
    Jan 2006
    Location
    Huntsville, AL
    My Bikes
    1973 Raleigh Superbe, 2006 Trek 4300 with no original parts, 1984 Ciocc, Custom Keith Anderson
    Posts
    1,283
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    0, there's an elephant in the way
    Quote Originally Posted by TechKnowGN
    San Jose has to be the most boring place I've ever been. And I live in Ohio.

  13. #13
    Feral Member Nicodemus's Avatar
    Join Date
    Apr 2004
    Location
    Roma, Italia
    My Bikes
    yes, I have one.
    Posts
    2,645
    Mentioned
    21 Post(s)
    Tagged
    0 Thread(s)
    Just use Lagrange
    Quote Originally Posted by KrisPistofferson View Post
    Did you just say "minarchist?" I'm going to start a 10-page vaginathon because only Libertarians can define Libertarianism. Also, you're mean.

  14. #14
    J3L 2404 gbcb's Avatar
    Join Date
    Mar 2006
    Location
    Shanghai
    My Bikes
    2007 Jamis Nova
    Posts
    1,069
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by polara426sh


    Awesome.

  15. #15
    Videre non videri
    Join Date
    Sep 2004
    Location
    Gothenburg, Sweden
    My Bikes
    1 road bike (simple, light), 1 TT bike (could be more aero, could be lighter), 1 all-weather commuter and winter bike, 1 Monark 828E ergometer indoor bike
    Posts
    3,202
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    #1

    Get some squared paper and make a scale drawing of Tarzan and the vine, with the angle as accurate as you can make it (and in getting it as accurate as possible, you'll hopefully realise what to do with the 37° angle, and why it is important).

    Then think about what Ken B. wrote in his post earlier.

  16. #16
    la vache fantôme phantomcow2's Avatar
    Join Date
    Aug 2004
    Location
    NH
    Posts
    6,266
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Have you taken trig yet? Remember that lovely energy balance? PE+KE = PE' + KE'
    Where PE is potential energy (m*g*height) and KE is Kinetic Energy (1/2mv^2), and ' means after the event has occurred.

    Use your trig knowledge to determine the height of the guy. You've got a side, and an angle.

    As with all of these types of projectile motion problems, you don't need mass. Not including mass always throws off a portion of students, always.
    C://dos
    C://dos.run
    run.dos.run

  17. #17
    la vache fantôme phantomcow2's Avatar
    Join Date
    Aug 2004
    Location
    NH
    Posts
    6,266
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Gravity is -9.81m/s^2
    But you can round to 10
    C://dos
    C://dos.run
    run.dos.run

  18. #18
    Crazy Kitty (male)
    Join Date
    Sep 2006
    Location
    In the awkward silence of a conversation.
    My Bikes
    Tricycle
    Posts
    0
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by phantomcow2
    Gravity is -9.81m/s^2
    But you can round to 10
    Double posting liar!
    Use the 9.81, accuracy is your friend.
    I'll give you a tip, Phantom measures with his thumbs.

  19. #19
    Crawlin' up, flyin' down bikingshearer's Avatar
    Join Date
    Jan 2006
    Location
    Democratic Peoples' Republic of Berkeley
    My Bikes
    1967 Paramount, 1982-ish Ron Cooper,1986 De Rosa Professional, 1978 Eisentraut "A," 1961 BianchiCompetizione, 1994 Trek 520, 199? Burley Bossa Nova
    Posts
    2,988
    Mentioned
    1 Post(s)
    Tagged
    0 Thread(s)
    9.8 m/s^2 - it's not just a good idea, it's the law!
    "I'm in shape -- round is a shape." Andy Rooney

  20. #20
    riding once again jschen's Avatar
    Join Date
    Oct 2005
    Location
    San Diego, CA
    My Bikes
    '06 Cervelo R3, '05 Specialized Allez
    Posts
    7,360
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Carry symbolic values as long as possible. Acceleration due to gravity is +g or -g, depending on how you orient your axis. Don't worry about the value of g until you have solved the problem symbolically.
    If you notice this notice then you will notice that this notice is not worth noticing.

  21. #21
    Senior Member SirScott's Avatar
    Join Date
    Jul 2005
    Location
    Littleton, CO
    Posts
    206
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    e =mc^2 solves everything.
    FTW Racing Crew

  22. #22
    '05 NUEser EJ123's Avatar
    Join Date
    Aug 2005
    Posts
    3,374
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Got there this morning and did the conservation equation, and all is good now.

  23. #23
    la vache fantôme phantomcow2's Avatar
    Join Date
    Aug 2004
    Location
    NH
    Posts
    6,266
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    So, whats the answer?
    C://dos
    C://dos.run
    run.dos.run

  24. #24
    riding once again jschen's Avatar
    Join Date
    Oct 2005
    Location
    San Diego, CA
    My Bikes
    '06 Cervelo R3, '05 Specialized Allez
    Posts
    7,360
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by EJ123
    did the conservation equation
    Either my physics is no good or they sure don't teach it the way they used to. I have no clue what you just said.
    If you notice this notice then you will notice that this notice is not worth noticing.

  25. #25
    la vache fantôme phantomcow2's Avatar
    Join Date
    Aug 2004
    Location
    NH
    Posts
    6,266
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    Quote Originally Posted by jschen
    Either my physics is no good or they sure don't teach it the way they used to. I have no clue what you just said.
    I think he is talking about conservation of energy. We call it the energy balance in my class. It's
    PE+KE = PE' + KE'
    Where PE' and KE' is the PE and KE after the event has occured. And of course, he is just solving for v'
    C://dos
    C://dos.run
    run.dos.run

Page 1 of 2 12 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •