Fundamentally, this problem is asking about the acceleration of a magnet and a piece of scrap iron with some extra mass attached to them—the other details are just to make sure there's no other net force acting on them.
As usual with forces problems, there's a set of steps we'll follow:
For this problem, we know there's no motion in the vertical direction (they're on a level surface), so our equation for Step 2 is just going to be ∑Fx = ma.
A black aluminum glider floats on a film of air above a level aluminum air track. A strong magnet is attached to the top of the glider, forming a total mass of 240 g. Aluminum feels essentially no force in a magnetic field, and air resistance is negligible.
A piece of scrap iron attached to one end stop on the track attracts the magnet with a force of 0.823 N when the iron and the magnet are separated by 2.50 cm.
(a) Find the acceleration of the glider at this instant.
(b) The scrap iron is now attached to another green glider, forming total mass 120 g. Find the acceleration of each glider when the gliders are simultaneously released at 2.50-cm separation.