Question

(a) A man weighing 779 N lies on a bed of nails. Find the average pressure exerted by a nail on his skin if there are 1010 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 5.60 N

Answer 1

(a) The average pressure exerted by a nail on his skin which is given as :

using an equation,    P = F / A

where, F = force = 779 N

A = Area of nail = n $\pi$ r²

then, we have

P = (779 N) / (1010) [(3.14) (0.5 x 10^-3 m)²]

P = (779 N) / (792.8 x 10^-6 m²)

P = 0.982 x 10⁶ N/m²

P = 9.82 x 10⁵ Pa

(b) The pressure exerted on the skin by an acupuncture needle which is given as :

using an above eq.

P = F / $\pi$ r²

then, we have

P = (5.6 N) / [(3.14) (0.1 x 10^-3 m)²]

P = (5.6 N) / (0.0314 x 10^-6 m²)

P = 178.3 x 10⁶ N/m²

P = 1.78 x 10⁸ Pa