Question 1198126
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The weight of the box is  3*10 = 30 newtons.


The static friction force is   30*0.4 = 12 newton.


It is less than the applied force of  15  newtons - hence, the box is moving, 
and the kinetic friction force is applied;  its value is  30*03 = 9  newtons.


Thus the net force is the difference    15 N - 9 N = 6 N.


<U>ANSWER</U>.  &nbsp;&nbsp;The net force is &nbsp;6 &nbsp;N.
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