Question

describe the difference in the way a magnetic field responds to a ferromagnetic object such as iron and plastic

Answer 1

The ferrromagnetic material has magnetic moments in various magnetic domains oriented in such a fashion that the net moment is zero. When an external magnetic field is applied on the ferromagnetic material all the moment align themselves in the direction of magnetic field. This makes the object magnetic although temporariry.

In case of the plastic, they are non magnetic material and no such magnetic moment exist in these plastics. So there is no impact of magnetic field on such objects. But magnetic do pass through them. They are never blocked. So plastic material remain non-magnetic.