Write an equation that expresses the following relationship. u varies jointly with p and d and inversely with w in your equation, use k as the constant of proportionality.

Let's explain what direct and indirect variation mean:

for some nonzero constant that is the constant of variation or the constant of proportionality.

for some nonzero constant , where is also the constant of variation.

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In this problem, varies jointly with and and inversely with , being the constant of proportionality, then:

since you're a real machine, your ama is always less than your ima, because you can never totally eliminate friction.