(a) A man weighing 720 N lies on a bed of nails. Find the average pressure exerted by a nail on his skin if there are 1210 nails and the flattened point on each nail has a radius of 0.500 mm.
(b) Calculate the pressure exerted on the skin by an acupuncture needle of radius 0.100 mm applied with a force of 5.20 N.