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PhysicStud01
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Homework Statement
Homework Equations
The Attempt at a Solution
please help with this question.
actually, i can't even understand it. so, please try to help with this questionNascentOxygen said:The template has yet to be filled in ...
Relevant equations??
Your attempt??
ok. sorry. when i tried again, i could do the calculations partCWatters said: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?
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',PhysicStud01 said:i needed to explain whether acceleration and velocity can be in different directions. f
well, these parts about directions of acceleration and force - i already explained.NascentOxygen said: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',
would that suffice for 6 points?NascentOxygen said:I don't know what answer they are looking for, but maybe noise, vibration, or heat buildup?
during my calculations, i found times (for the forces) to be 8.66ms and 2.88msNascentOxygen said: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?
can you be a bit more clear. i can't get what you are trying to say here?CWatters said: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?
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?PhysicStud01 said:there's only the last part that i can't answer right now.
I believe PhysicStud01 did all that successfully to arrive at the answer in post #11.S.Bhattacharyya said: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.
haruspex said:I believe PhysicStud01 did all that successfully to arrive at the answer in post #11.
i've solved the problem. only the part o=about physical problems, ... i can't figureS.Bhattacharyya said:Oh that's good...I failed to notice. Well then I guess PhysicStud01 has solved his probem :)
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.S.Bhattacharyya said: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.
haruspex has put it in a good way...just have a closer look at the quoteharuspex said:For speeding it up, based on your equations, which data modified in which directions, would increase the print speed?
CWatters said: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?
PhysicStud01 said:can you be a bit more clear. i can't get what you are trying to say here?
I thought of that, but shouldn't that be part of the 8ms already specified for how long it takes to print the character?CWatters said:you might have to allow a "settling time" for oscillation to die away
by the way, I've been thinking. Are the magnitudes of the accelerating and retarding forces realistic to be produced in a printer? Or are they too large? Maybe that's oneof the restraints? What do you think? I don't know whether the forces are realistic or not thoughS.Bhattacharyya said:Strictly speaking from the questions perspective perhaps the force acting to accelerate the printer could be increased, the actual head could be made lighter so it accelerates faster...etc (gosh am I breaking any guidelines!?)
so, as a reason, may I say that allowing the head to move at constant speed would be quicker? this involves less mechanical work (I think) - there won't be a need to produce forces that causes accelerations and decelrations - so less friction, less heat, ...CWatters said:The old fashioned "golf ball" type printers may have worked like this but I don't think modern inkjet printers do. The latter just move the head at a constant speed from one edge of the page to the other. They don't stop the head to print a character they just print dots "on the fly". Those dots can form part of a picture or a character. eg there is nothing special about characters to a modern injet printer.
but won't increasing the forces to cause greater accelerations have other drawbacks. How can the force be increased actually?CWatters said:Yes and no. Yes it would make the printer quicker but part iv is really trying to test your knowledge of physics rather than your ability to redesign the printer. They are telling you that the head accelerates, decelerates and stops. I think you are over thinking this.
For example if redesigning the whole printer from a golf ball to an inkjet was a valid answer then it might be equally valid to suggest replacing the entire printer with an industrial printing press capable of printing a few million newspapers a day.
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