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An application of Dynamics, very difficult, really need help

  1. Dec 31, 2014 #1
    1. The problem statement, all variables and given/known data
    pic.png

    2. Relevant equations


    3. The attempt at a solution
    please help with this question.
     
  2. jcsd
  3. Dec 31, 2014 #2

    NascentOxygen

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    The template has yet to be filled in ...

    Relevant equations??

    Your attempt??
     
  4. Dec 31, 2014 #3
    actually, i can't even understand it. so, please try to help with this question
     
    Last edited by a moderator: Jan 4, 2015
  5. Dec 31, 2014 #4

    CWatters

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    Which bit don't you understand?
    Try describing the motion of the print head in your own words.

    PS: Forum rules don't allow us to solve homework for you. We can only help you solve it by giving hints or correcting errors in your own attempt.

    I'm sure you understand at least some of the problem statement. ..You know what a print head is? You know it has mass? You know masses accelerate when forces are applied to them? You may have heard of Newton's laws or the equations of motion?
     
    Last edited: Dec 31, 2014
  6. Jan 2, 2015 #5
    ok. sorry. when i tried again, i could do the calculations part

    but can you explain to me the part iv. I got a lot of problems with the applications part. the only info I know about it is what is mentioned in the question

    and also, for part (a), i needed to explain whether acceleration and velocity can be in different directions. for part (b), I had to explain whether resultant force and acceleration can be in different directions.
    i think they should be related.

    + that part is 6 points. so, I don't think it's a simple reason.

    so, please help me with that part
     
    Last edited by a moderator: Jan 4, 2015
  7. Jan 2, 2015 #6

    NascentOxygen

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    When a ball is thrown up in the air, its velocity for a while is directed upwards, yet all the time its acceleration is g, and that's directed downwards. A moving object can be brought to rest if you give it an acceleration opposite in direction to its velocity',
     
  8. Jan 2, 2015 #7
    well, these parts about directions of acceleration and force - i already explained.
    i was thinking may be they are related to the last part
    there's only the last part that i can't answer right now.
    thanks anyway
     
  9. Jan 2, 2015 #8

    NascentOxygen

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    I don't know what answer they are looking for, but maybe noise, vibration, or heat buildup?

    Perhaps something to do with the time required to start/stop/measure the ink flow to each dot?
     
    Last edited: Jan 2, 2015
  10. Jan 2, 2015 #9
    would that suffice for 6 points?
    can you come up with a suitable reason that could be linked with parts i, ii and iii and the parts a and b that i mentioned (relations between directions of accelration and velocity and force and acceleration)
     
  11. Jan 2, 2015 #10
    during my calculations, i found times (for the forces) to be 8.66ms and 2.88ms
    does this help???
     
  12. Jan 2, 2015 #11
    ii was 11.5 millisec
    and iii was 51.2 per sec

    anyone please?
     
    Last edited by a moderator: Jan 4, 2015
  13. Jan 2, 2015 #12

    CWatters

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    for iv) the most obvious thing is the actual time to print the character once the head has stopped moving.

    As for what would you change to make printing faster... What factors effect how fast the print head accelerates?
     
  14. Jan 3, 2015 #13
    can you be a bit more clear. i can't get what you are trying to say here?
     
  15. Jan 3, 2015 #14
    anyone please. can you suggest your ideas.
    and how can changes be made to increase the speed?
     
    Last edited by a moderator: Jan 4, 2015
  16. Jan 4, 2015 #15

    haruspex

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    It's an ugly question. You've calculated the print speed based on the data given. Why might it print more slowly? Because the data provided are unreliable?
    If it is, e.g., a matter of heat build up, then the data should have been qualified, something like "in tests of printing a few characters..."

    For speeding it up, based on your equations, which data modified in which directions, would increase the print speed?
     
  17. Jan 4, 2015 #16
    Well, they've given you the mass, the forces and the distance the head needs to cover. You've got to know that everytime the printer gets ready to print a character, it's velocity is zero. But, force acts on it AFTER printing the character, so then you've got to calculate the velocity it attains while covering the distance to the next character (2.5 mm) just before the retarding force stops it again to zero velocity. So all you've got to worry about is one cycle of 'printing, moving and stopping', the graph will repeat itself. Use Newton's laws of motion with the proper signs for acceleration and you will get all the skeleton data required. The last part of the question is a real world scenario given to you, they've asked you for physical conditions, so perhaps it could be friction, heating, mechanical advantage loss due to improper parts and all that kind of stuff. So then you know what changes you have to make.
     
  18. Jan 4, 2015 #17

    haruspex

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    I believe PhysicStud01 did all that successfully to arrive at the answer in post #11.
     
  19. Jan 4, 2015 #18
    Oh that's good.....I failed to notice. o0) Well then I guess PhysicStud01 has solved his probem :)
     
  20. Jan 4, 2015 #19
    i've solved the problem. only the part o=about physical problems, ... i can't figure
    as for the calcualtions, it's ok
     
  21. Jan 4, 2015 #20
    I don't think there are any calculations involved....the numerical answer you computed only works in ideal situations (like zero friction, drag, etc). The answer to the last part must be qualitative not quantitative because they haven't given you any data to compute losses in speed due to the so called 'physical conditions'. So you've got to think of the real world and figure out what makes the printer work slower and suggest necessary changes.
     
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