Answer
The linear mass density of the cord is $3.8~grams/meter$
Work Step by Step
We can find the linear mass density of the cord:
$v = \sqrt{\frac{F}{m/L}}$
$v^2 = \frac{F}{m/L}$
$\frac{m}{L} = \frac{F}{v^2}$
$\frac{m}{L} = \frac{75~N}{(140~m/s)^2}$
$\frac{m}{L} = 0.0038~kg/m$
$\frac{m}{L} = 3.8~g/m$
The linear mass density of the cord is $3.8~grams/meter$
