Complete Question
The complete question is shown on the first uploaded image
Answer:
The net force is  [tex]F_{net}= 6.44 *10^{-4} N[/tex]
Explanation:
Generally the net force is a force that come up due to the unequal centripetal force(A difference in centripetal force ) and it is mathematically represented  as
           [tex]F_{net} = \Delta F_{cen}[/tex]
and the difference in centripetal force  [tex]\Delta F_{cen}[/tex] is mathematically represented as
        [tex]\Delta F_{cen} = \Delta m* rw^2[/tex]
Which the difference in mass multiplied by the centripetal acceleration
 Substituting 10 mg = [tex]10 *10^{-3}g[/tex] for [tex]\Delta m[/tex] , 12 cm = [tex]\frac{12}{100} = 0.12m[/tex] for radius
 and  70,000 rpm = [tex]70,000 *[\frac{2 \pi rad}{1 rev}][\frac{1 min}{60s} ] = 7326.7 rad/s[/tex]
       [tex]F_{net} = \Delta F_{cen} = 10*10^{-3} * 0.12 * 7326.7[/tex]
           [tex]F_{net}= 6.44 *10^{-4} N[/tex]