Using Matlab to solve dynamics problem

  1. I've attached my problem set. I'm having an issue on how to write the formula to insert it into matlab. According to the problem set, dl/dt = 0.2m/s. I actually have the "solution" to the problem, though I don't understand why the answer is what it is. Basically, my instructor used the pythagorean theorem and set l[tex]^{2}[/tex] = b[tex]^{2}[/tex] + [tex]^{2}[/tex]. He then differentiated twice w.r.t time, hence dc/dt going to 0 (c is constant) and the second derivative of dl/dt going to 0 as well (dl/dt constant). The end result is d[tex]^{2}[/tex]b/dt[tex]^{2}[/tex] = (dl/dt)[tex]^{2}[/tex] - (db/dt)[tex]^{2}[/tex]. a (acceleration) is the second deriv of b evidently. Can anyone tell me the reason behind differentiating twice, also how I could possibly use that formula in matlab? Thanks.
     

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