A motor cyclist without a face mask has his mouth facing dir

A motor cyclist without a face mask has his mouth facing directly forward and hence breathes in and out at the stagnation point. Determine at what speed the stagnation pressure would be so great as to prevent the rider from exhaling (and possibly suffocating). Assume that his maximum breathing out pressure is equivalent to 100mm water gauge. Hint: Use energy equation.

Solution

For stagnation decrease in pressure due to speed should be equivalent to maximum breathing out presure.

(1/2)x(Air desnity)x(Speed)2 = 100 X10-3 x (Water Density)x 9.8

Air desnity = 1.225 Kg/m3

Water density = 1000 Kg/m3

Speed = 40 m/s