A ductile material has the properties Syu = 62 psi and Syc = 78 psi. Using the ductile Coulomb- Mohr theory, determine the factor of safety for the states of plane stress: a) σx = 20 ksi, σy = 15 ksi
b) σx = 15 ksi, σy = −20 ksi
c) σx = 20 ksi, τxy = −15 ksi
d) σx = −10 ksi, σy = 15 ksi, τxy = −10 ksi
e) σx= −24 ksi, σy = −20 ksi, τxy = −15 ksi

Apreheater involves the use of condensing steam at 100°c on the inside of a bank of tubes to heat air that enters at 1 atm and 25°c. the air moves at 5 m/s in cross flow over the tubes. each tube is 1 m long and has an outside diameter of 10 mm. what is the minimum value of nl needed to achieve an outlet temperature of t 75 c? what is the corresponding pressure drop across the tube bank?