I got almost full marks in a differential calculus question even though I got the answer wrong.
Basically I'd used the wrong number at the start of the question but worked the answer right for the number I used. At the end of the exam I checked the answers and spotted the mistake. I wrote this down estimated the right answer (nearly correct!) and got nearly full marks!!
First of all, physics exams are more about the process of getting the answer rather than the actual answer. Having said that if she didn't instruct you to use a specific formula in writing on the question you can use any formula you want. Well that's how it is in Australia anyway.
The equation or expression used (submitted) by you is incorrect and your teacher is right. Any expression where one variable equals the sum of two other variables related by a set formula (like the relation between say, amps/volts/watts) is defined as an exact equation that can’t be manipulated in the way you suggest, even if it produces the correct answer in this instance.
The equation might be totally wrong or missing something, but to prove this means that you have to provide the necessary logic using the original formula and complex mathematics that were necessary to prove it in the first place.
The reason why things are expressed in the notation a = b-c (or whatever) is very important as it has traversed the path of complexity to arrive at a situation where an exact relationship between three objects has been defined. This gives you the power to work out very simply (given any of the two variables) what the missing variable is. That’s why these systems are used. They are not perfect but rules of thumb and have been in constant use for more than sixty years.
Posted by BenQuilter
Sazar, would you not agree though that the two equations (vf=vi+at, and vf=vi-gt) are exactly the same thing? (its just that the acceleration was not given in the problem becuase it was a known constant, but is it not still accleration, and thus using a is just as good as g?).
and 1 more thing. she said it should be vf=vi-gt. now if she expected the g to have a "-" value (which she seemed to have), would not the problem be transformed into vf=vi-(-g)t, and thus turned into vf=vi+gt?
I am an 16 years old boy, I study physics, but we take a much much harder thing, for Example Archimede's principle "the three states of it", Surface Tension, Mechanical waves and Electromagnetic waves, the steady flow, the Turbulent flow, and a lot more, anyone understand anything? I don't!