- #1

Grand

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## Homework Statement

I'm reading Classical mechanics by Morin and I can't understand the following reasoning. There is a horizontal stick at the ends of which 2 forces [tex]F_1[/tex] and [tex]F_2[/tex] are applied perpendicular and upward to the stick, and another force [tex]F_3[/tex] applied downward and again perpendicular to the stick. The distances from the point where [tex]F_3[/tex] is applied to the ends of the stick are [tex]a[/tex] and [tex]b[/tex]. Now the author proves that [tex]F_3a=F_2(a+b)[/tex] by saying that since the force is linear, then the following must hold:

[tex]F_3f(a)=F_2f(a+b)[/tex]

where f is a function to be determined. I can't fully understand this reasoning, so could anyone give me some more detail. I'll be very grateful.

Greetings,

Grand