This is the concept of proportionality. To solve the above question we proceed as follows;
let distance be d, weight be w. Thus;
dαw
hence;
h=kw
where;
k is constant;
if the string stretches 9 inches when weight of 100 pounds is places the the formula will be:
9=100k
thus;
k=9/100=0.09
hence;
d=0.09w
The length of the string when 90 pounds is placed will be:
d=0.09(90)
d=8.1 inches
