When an object is under free fall then it means the net force on the object is only due to gravitational attraction force
So here we have
[tex]F_{net} = mg[/tex]
so in order to find mass we can use
[tex]m = \frac{F_{net}}{g}[/tex]
here given that net force on the object is
F = 170 N
[tex]m = \frac{170}{9.8}[/tex]
[tex]m = 17.35 kg[/tex]
so the mass of the object must be 17.35 kg
