Creating a Solar Model - Excel Help

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The discussion revolves around calculating values for columns I and J in a solar model using Excel. The user is experiencing issues with negative outputs when they expect values to approach 1. Suggestions include adding parentheses around the calculation of B3-B2 and questioning the necessity of the SUMPRODUCT function, which may not be needed for single cell calculations. The user expresses frustration with their lack of Excel knowledge and the professor's expectations. The conversation emphasizes troubleshooting Excel formulas to achieve correct results.
PeteWheatstraw
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Homework Statement



The problem given is...Calculate mI+1 and lI+1 at point xI+1 using equation (5), the values of the slopes at points xI+1 and xI from equation (4), and the values of mI and lI from the previous step.

Here is a screenshot of my solar model

solarmodel_zps169d03c0.png


Homework Equations



solarmodel2_zps8032b590.png

The Attempt at a Solution



I need help with columns I and J.

For column I, I have the equation entered as =SUMPRODUCT(I2+1/2*(G3+G2)*B3-B2)

For J I have =SUMPRODUCT(J2+1/2*(H3+H2)*B3-B2)

and for some reason I'm getting negative values when as it goes down it should be getting closer to 1

Thanks in advance!
 
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You need parentheses around B3-B2.
(Why do you need to use sumproduct? You're not using entire arrays of numbers to calculatd a single cell, are you?)
 
haruspex said:
You need parentheses around B3-B2.
(Why do you need to use sumproduct? You're not using entire arrays of numbers to calculatd a single cell, are you?)

Thank you so much! I knew it was something obvious that would make me look stupid ;)

To your question...I'm not really sure. I'm excel illiterate and our professor expects us to use it without ever showing us anything.
 
PeteWheatstraw said:
To your question...I'm not really sure. I'm excel illiterate and our professor expects us to use it without ever showing us anything.

Try removing the SUMPRODUCT() wrapper. I don't think it's doing anything.
 
Thread 'Variable mass system : water sprayed into a moving container'

Thread 'Variable mass system : water sprayed into a moving container'

Starting with the mass considerations #m(t)# is mass of water #M_{c}# mass of container and #M(t)# mass of total system $$M(t) = M_{C} + m(t)$$ $$\Rightarrow \frac{dM(t)}{dt} = \frac{dm(t)}{dt}$$ $$P_i = Mv + u \, dm$$ $$P_f = (M + dm)(v + dv)$$ $$\Delta P = M \, dv + (v - u) \, dm$$ $$F = \frac{dP}{dt} = M \frac{dv}{dt} + (v - u) \frac{dm}{dt}$$ $$F = u \frac{dm}{dt} = \rho A u^2$$ from conservation of momentum , the cannon recoils with the same force which it applies. $$\quad \frac{dm}{dt}...
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