Discuss how electromagnets have been created that are strong enough to pick up cars in a wrecking yard and are able to be switched off, dropped the cars onto a scrap pile to be crushed.

An inductor is just a coil of wire with magnetic properties. It is a device that stores electromotive force or energy in the form of magnetic field.  A current yields a magnetic field around it through a conductor. The pattern of flux for this magnetic field would be the number of concentric circle perpendicular to the detection of current. The capacity of the inductor is affected by the number of coils which would give more inductance, the material that is used for the coil, the cross sectional area of the coil and the length of the coil. For instance you have an 8 meters diameter coil with seven loops of wire. You place the coil on an area where there is a parked car. The inductance of the coil will be much larger compared to the coil without a parked car nearby because of the presence of the steel from the car. It changes the magnetic field of the coil because it acts as a core of the inductor.

Answer: The complementary relationship indicated by the Newton's second law...

For a given applied force the acceleration of the trolley is inversely proportional to it's mass.