The third object from the given problem has a net force of - 68 Newtons because there is no net vertical force action of this object as equal upward and downward forces cancel each other.
What is Newton's second law?
Newton's Second Law states that The resultant force acting on an object is proportional to the rate of change of momentum.
F = m*a
The net vertical force = 27 Newtons - 27 Newtons
= 0 Newtons
The net vertical force on the object would be zero.
The net horizontal force acting on the object = - 102 Newtons + 34 Newtons
= -68 Newtons
Hence we can conclude that the net force of - 68 Newton acting on the third object.
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