1. Calculate the net force:

* Net force (F_net) = mass (m) * acceleration (a)

* F_net = 50 kg * 9 m/s²

* F_net = 450 N

2. Calculate the friction force:

* Friction force (F_friction) = Applied force (F_applied) - Net force (F_net)

* F_friction = 500 N - 450 N

* F_friction = 50 N

Therefore, the friction force acting on the box is 50 Newtons.