The floor on a dance hall can take a pressure of 3.5MPa before getting damaged. A lady of mass 60kg wears high heeled shoes. What is the smallest area of the sole of a heel she could wear such that it won't permanently damage the floor

smallest area of the heel is 0.000168  m^2

Explanation:

Recall that pressure is defined as: Force / area. Therefore to reach a pressure of 3,500,000 Pa using a force: m * g = 60 kg * 9,8 m/s^2 = 588 N, one needs:

Area = 588 / 3500000 m^2 = 0.000168  m^2

the answer is the first electromagnet (a). this is because it has more coils around the ferromagnetic material. increasing the number of coils increases the surface area in which the metal interacts with the current in the coil. this enables more atoms in the metal to become aligned hence becoming more magnetized.