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 Apr 2 awarded Notable Question Mar 12 awarded Notable Question Apr 20 comment How to find $p(t)$ when $m$ varies linearly with $t$? @YvesDaoust Thank you for reminding me of the title. My original problem is a bit more complex, and this question is very simplified, which is why, after simplifying the question a lot, it turned out to be a simple differential equation, not what the title originally stated (as Tom-Tom wrote in his answer). Now it is just a matter of rewriting my original equation as a differential equation. I guess I must learn how to express my problems in a more simple manner to be able to solve them more easily. Apr 20 revised How to find $p(t)$ when $m$ varies linearly with $t$? clarified the question Apr 20 revised How to find $p(t)$ when $m$ varies linearly with $t$? clarified the question and made it more useful for Googlers Apr 20 comment How to find $p(t)$ when $m$ varies linearly with $t$? Updating the question to clarify now, thank you. Apr 20 revised How to find $p(t)$ when $m$ varies linearly with $t$? clarified the question where it was unclear, and cleaned it up to make it more useful to Googlers Apr 20 comment How to find $p(t)$ when $m$ varies linearly with $t$? @YvesDaoust The mass decreases as time passes. The mass isn't defined based on what $t$ is at $p=p(t)$. I might have been a bit unclear in the question. Apr 20 comment How to find $p(t)$ when $m$ varies linearly with $t$? Now I understand why the sum doesn't work. Since the time is squared, it increases much faster than the mass decreases, so that the limit when $k \to \infty$ does not resemble the correct position. Do you agree? Apr 20 accepted How to find $p(t)$ when $m$ varies linearly with $t$? Apr 20 revised How to find $p(t)$ when $m$ varies linearly with $t$? added 16 characters in body Apr 20 comment How to find $p(t)$ when $m$ varies linearly with $t$? I have an object that is pushed by a force $F$. As time passes, the mass of the object decreases, so that over time the acceleration of the object increases. What I was thinking was that for an infinitesimal timeframe, the difference in $p$ is given by what is inside the summation in the question. So by letting $\lim_{k→\infty}$ I would expect to get the actual $p$. Apr 20 comment How to find $p(t)$ when $m$ varies linearly with $t$? Thank you for such an in depth answer! The second case is the one I was trying to solve. I was just trying to solve the problem in the wrong way. Apr 20 asked How to find $p(t)$ when $m$ varies linearly with $t$? Aug 19 awarded Popular Question Jul 2 awarded Curious Apr 19 awarded Popular Question Dec 7 comment Is there one method of adding and subtracting without a calculator? Yes, but $80-(-70)$ would by my algorithm be interpreted as $80+70$ since, as I see it, this method cannot be applied without running a else/elseif for these four conditions: +A+B, +A-B (|A|>|B|?), -A+B, -A-B. Dec 7 comment Is there one method of adding and subtracting without a calculator? It probably is correct. I'm going to test my algorithms with a recursive fibonacci generator, so if the numbers are correct, the algorithms are probably correct as well. Dec 7 comment Is there one method of adding and subtracting without a calculator? Hmm... I've been calculating on a paper for a while now. As I see it, one can make a few rules. If you always do A-B. Given A-B where |A|>|B|. One can calculate with as many digits as the number with the most digits, and then neglect all the 1's in the answer to get the right answer.