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Find the initial velocity of a man falling in a boat

  1. Apr 28, 2016 #1
    • Thread moved from the technical forums, so no HH Template is shown.
    Warren falls over his tackle box and lands in a canoe 0.95 m below the side of the dock. Warren's mass is 70 kg and the canoe has a mass of 72 kg. Warren and the canoe move 1.73 m away from the dock in 1.005 seconds.

    relating equations are
    Vi = Vf - at
    v = d/t
    A = change in velocity/time interval

    Work
    I was thinking that I would need to take the the velocity from the end of the problem which is 1.73 m /1.005 s = 1.72 m/s. I think that is my Vf, i just want to make sure that is correct. Because if it was the Vf i still need to find the acceleration. Any help would be appreciated.
     
  2. jcsd
  3. Apr 28, 2016 #2
    What happens when Warren hits the canoe? Have you studied collisions?
     
  4. Apr 28, 2016 #3
    As per the event pl. state what you wish to know? apart from given data the 'falling' part is important -how he fell verically down or in a curved path?
     
  5. Apr 28, 2016 #4
    That is the exact question and all of the information, it only asks me to find the initial velocity, that's why i am coming here because i was hoping some people who are good a physics can help me get past this question.
     
  6. Apr 28, 2016 #5
    i hope it is initial velocity of the canoe?

    it appears that there was collision of the two and momentum of canoe changed- the man was on the tackle box and he fell and provided a push to the boat
    he fell through a height h so he must have transferred his potential energy to a velocity of fall and ultimately his momentum to the canoe.
    so now you can proceed using conservation of momentum.

    if you are a physics student you know momentum is a vector so one will ask at what angle he fell and hit the canoe?

    well one can not fill in the missing words 'of a question' that will be 'guessing' the thing actually happening.
     
  7. Apr 28, 2016 #6

    haruspex

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    Brady, please provide the complete and exact question, word for word, as given to you.
     
  8. Apr 29, 2016 #7
    it's sad to say that is the entire problem, i constantly struggle in the class but i don't think it is because of the subject, the highest grade on our most recent test was a 70%, i don't usually go online asking for help but when it comes to this worksheet i really am in disbelief on how hard it is, i'm a senior in a CP physics class, i usually am a 3.5 student and i study my a$$ off for this subject and still can't keep a C. If it really is that bad i'll just confront her about it
     
  9. Apr 29, 2016 #8
    What do you mean "entire problem"? As written in the OP there is no question asked.
     
  10. Apr 29, 2016 #9

    jbriggs444

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    To amplify on this, when you put part of the problem statement in the title of a message, you should still include that portion in the body of the message. The body should be complete and able to stand on its own. It must not depend on the thread title for context or for details.
     
  11. Apr 29, 2016 #10

    haruspex

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    ok.
    Here are the ambiguities that I see. What moment in the process does "initial" refer to? Before he tripped, nearly zero. So probably it means just before he hit the boat.
    What does velocity refer to? It's often used, sloppily, just to ask for speed. If so, is it the total speed (which we could get from the height fallen, if only we knew the height of the man's mass centre before he fell) or just the horizontal component (which we can get from conservation of momentum and the speed of the boat after landing)?
    In each of those cases, we only need some of the information given. If it really means velocity, as in magnitude and direction, then we need to figure out both of those.
    Putting all that together, my guess is it really is asking for velocity, but you don't quite have enough information. You will have to assume the height given is the height through which the man's mass centre falls.
     
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