Question 1204635
f, the force needed
r, the curve radius
w, the car's weight
s, speed of car
k, variation constant


This is what the description becomes literally, in variables------{{{f=((ws^2)/(r))k}}}


Your question gives these as values and asks for so you can determine value for k.
{{{system(f=640,r=650,w=2600,s=40)}}}.

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