A 25N sideways force is applied to a 10kg box moving at a constant speed of 5 m/s. The discussion clarifies that if the box is moving with constant velocity, the net force acting on it is zero, indicating no acceleration. The presence of friction was questioned but not confirmed, suggesting it may not be a factor. The hint provided encourages careful consideration before applying equations. Ultimately, the conclusion is that the net force is zero due to the absence of acceleration.