pressure

A hammer head with mass 0.5 kg strikes the head of a nail at a speed of 10m/s .The nail is driven 1 cm into a piece of wood. What is the average force on the nail?

The weight of a rider, driving scooter is assumed to be evenly distributed on both the tyres. The area of contact of each type with the ground is 10 cm2. If the pressure inside the tyres is 3 bar, find the mass of the rider (g = 10 ms−2)

a small block is pulled along a rough horizontal surface at a constant speed of 3m/s by a constant force. The magnitude of the force is 30N and acts at an angle of 30 degrees to the horizontal. Calculate the work done by this force in 10 seconds

What is friction?

I understand the concept of electricity well but I'm not able to understand what is exactly going on inside a magnet. I don't understand what creates the magnetic effect of a magnet. How can electricity be generated from magnet and magnet be generated from electricity? What is really going on in terms of atoms and charges and everything?

A 100N girl rides a 50N bicycle a total of 150m at a constant speed. The frictional force against the forward motion of the bicycle equals 25N. How much work does the girl do? Explain your answer.