Engineering Dynamics Problem

I might suggest you create a name TotWeight since you use that a lot. and i think you want to be using time change so cell B3 should be something like =D2*(A3-A2) but then again you can define dt as a name since it is a constant (you could make it =$A$3-$A$2 so if you change the step size it will automatically change with it. Another nice option is to define "Time Step" on the sheet (e.g. F1="Time Step =" and then in G1 you type what it will be like 0.02). And another quick trick/tip, with G1 highlighted you can click on the cell address in the top let to the left of the formula bar where is says 'G1' and then type "dt" and that will automatically create a "Name" called "dt" and set it to cell G1. Then in A2 you can type =SEQUENCE(1000,,,dt) to automatically create a column of 1000 numbers stepping by 'dt'. If you don't want to start at 0 then use =SEQUENCE(1000,,dt,dt)
I'm not clear why acceleration is changing. What is velocity dependent? Basically I don't get where that 0.9*V^2 comes in (looks like 1/2 m v^2 but that would be work not acceleration). I'm guessing that is another part of the problem not noted here.
Also in your notes you combine mu1 F1 + mu2 F2 to be mu*m*g which seems fine if mu1=mu2 but in your name definitions you indicate mu1=0.1 and mu2=0.2 so are the names wrong or the formula?