How can a magnet be demagnetized ?

How are the molecular magnets of a magnet affected, when the magnet is demagnetized ?

A magnet can be demagnetised by

The coercitivity of a small magnet where the ferromagnet gets demagnetized is 3 xx 10^(3) Am^(-1) . The current required to be passed in a solenoid of length 10 cm and number of turns 100 , so that the magnet gets demagnetized when inside the solenoid , is :

The magnet can be completely demagnetized by

A bar magnet makes 40 oscillations per minute in an oscillation magnetometer. An identical magnet is demagnetized completely and is placed over the magnet in the magnetometer. Find the time taken for 40 oscillations by this combination. Neglect any induced magnetism.

Four situations I. A boy throws a ball up in the air and it falls freely on the ground. II. A horse pulls a cart and the cart moves forward. III. A can is opened with the help of an opener. IV. A magnet is demagnetized by hammering it. In which of the given situations is indirect application of force involved?