To practice Problem-Solving Strategy 5.1 Newton's First Law: Equilibrium of a Particle. Suppose that you want to move a heavy box with mass 30.0 kg across a carpeted floor. You try pushing hard on one of the edges, but the box does not move. Suppose that you are pushing against the box from an angle 30.0∘ above horizontal with a force of magnitude 240 N. What is the magnitude of the friction force acting on the box?